Search

S190426c / GW190426_152155 was the first probable neutron star - black hole merger candidate detected by the LIGO-Virgo Collaboration. We undertook a tiled search for optical counterparts of this event using the 0.7m GROWTH-India Telescope. Over a period of two weeks, we obtained multiple observations over a 22.1 deg^2 area, with a 17.5% probability of containing the source location. Initial efforts included obtaining photometry of sources reported by various groups, and a visual search for sources in all galaxies contained in the region. Subsequently, we have developed an image subtraction and candidate vetting pipeline with ~ 94% efficiency for transient detection. Processing the data with this pipeline, we find several transients, but none that are compatible with kilonova models. We present the details of our observations, working of our pipeline, results from the search, and our interpretations of the non-detections that will work as a pathfinder during the O4 run of LVK., 12 pages, 6 figures, Accepted for publication in Monthly Notices of the Royal Astronomical Society

We search for signatures of recent galaxy close interactions and mergers in a sample of 202 early-type galaxies in the local universe from the public SDSS Stripe82 deep images ($\mu_r \sim 28.5$ mag arcsec$^{-2}$). Using two different methods to remove galaxies' smooth and symmetric light distribution, we identify and characterize eleven distinct types of merger remnants embedded in the diffuse light of these early-type galaxies. We discuss how the morphology of merger remnants can result from different kinds of minor and major mergers, and estimate the fraction of early-type galaxies in the local universe with evidence of recent major (27%) and minor (57%) mergers. The merger fractions deduced are higher than in several earlier surveys. Among remnants, we find that shells are the dominant merger debris (54%) associated with early-type galaxies, resulting from both major and minor mergers, with those characteristics of major mergers being significant (24% of shell host galaxies). The most uncommon merger-related structures are boxy isophotes of the stellar distribution and the presence of disk fragments near the cores of galaxies. We develop a classification scheme for these fine structures that may be used to infer their likely genesis histories. The classification is primarily based on the mass ratios of the merged galaxies. This work, when combined with predictions from numerical simulations, indicates that most (if not all) early-type galaxies in the local Universe are continually evolving as a result of (minor) merger activities., Comment: Accepted for publication in MNRAS [with 9 Figures, 3 Tables]

Tidal disruption events (TDEs) are bursts of electromagnetic energy released when supermassive black holes at the center of galaxies violently disrupt stars that pass too close. TDEs provide a new window to study accretion onto supermassive black holes; in some cases, this accretion leads to launching of a relativistic jet, but the necessary conditions are not fully understood. Here, we report the optical discovery of AT2022cmc, a rapidly fading source located at redshift z=1.19325. Observations of a bright counterpart at other wavelengths, including X-rays, sub-millimeter, and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron ``afterglow.'' Using 4 years of Zwicky Transient Facility survey data, we calculated a rate of 0.02 ^{+ 0.04 }_{- 0.01 } Gpc^{-3} yr^{-1} for jetted TDEs based on the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X--ray and radio observations (Brown et al., 2015), confirming that ~1% of TDEs have on-axis jets. Forthcoming observations of AT2022cmc could resolve the jet through high-resolution imaging, while optical surveys have the potential to unveil a population of cosmological flares of the AT2022cmc class.

The astrophysical journal 932(1), 40 (2022). doi:10.3847/1538-4357/ac6c29, The Fermi Gamma-ray Burst Monitor (GBM) triggers on-board in response to ∼40 short gamma-ray bursts (SGRBs) per year; however, their large localization regions have made the search for optical counterparts a challenging endeavour. We have developed and executed an extensive program with the wide field of view of the Zwicky Transient Facility (ZTF) camera, mounted on the Palomar 48 inch Oschin telescope (P48), to perform target-of-opportunity (ToO) observations on 10 Fermi-GBM SGRBs during 2018 and 2020–2021. Bridging the large sky areas with small field-of-view optical telescopes in order to track the evolution of potential candidates, we look for the elusive SGRB afterglows and kilonovae (KNe) associated with these high-energy events. No counterpart has yet been found, even though more than 10 ground-based telescopes, part of the Global Relay of Observatories Watching Transients Happen (GROWTH) network, have taken part in these efforts. The candidate selection procedure and the follow-up strategy have shown that ZTF is an efficient instrument for searching for poorly localized SGRBs, retrieving a reasonable number of candidates to follow up and showing promising capabilities as the community approaches the multi-messenger era. Based on the median limiting magnitude of ZTF, our searches would have been able to retrieve a GW170817-like event up to ∼200 Mpc and SGRB afterglows to z = 0.16 or 0.4, depending on the assumed underlying energy model. Future ToOs will expand the horizon to z = 0.2 and 0.7, respectively., Published by Univ., Chicago, Ill. [u.a.]

We present the design and performance of the GROWTH-India telescope, a 0.7 m robotic telescope dedicated to time-domain astronomy. The telescope is equipped with a 4k back-illuminated camera giving a 0.82-degree field of view and sensitivity of m_g ~20.5 in 5-min exposures. Custom software handles observatory operations: attaining high on-sky observing efficiencies (>~ 80%) and allowing rapid response to targets of opportunity. The data processing pipelines are capable of performing PSF photometry as well as image subtraction for transient searches. We also present an overview of the GROWTH-India telescope's contributions to the studies of Gamma-ray Bursts, the electromagnetic counterparts to gravitational wave sources, supernovae, novae and solar system objects., 17 pages, 8 figures, Accepted for publication in The Astronomical Journal

The many unusual properties of the enigmatic AT2018cow suggested that at least some subset of the empirical class of fast blue optical transients (FBOTs) represents a genuinely new astrophysical phenomenon. Unfortunately, the intrinsic rarity and fleeting nature of these events have made it difficult to identify additional examples early enough to acquire the observations necessary to constrain theoretical models. We present here the Zwicky Transient Facility discovery of AT2020xnd (ZTF20acigmel, the 'Camel') at z = 0.243, the first unambiguous AT2018cow analogue to be found and confirmed in real time. AT2018cow and AT2020xnd share all key observational properties: a fast optical rise, sustained high photospheric temperature, absence of a second peak attributable to ejection of a radioactively heated stellar envelope, extremely luminous radio, millimetre, and X-ray emission, and a dwarf-galaxy host. This supports the argument that AT2018cow-like events represent a distinct phenomenon from slower-evolving radio-quiet supernovae, likely requiring a different progenitor or a different central engine. The sample properties of the four known members of this class to date disfavour tidal disruption models but are consistent with the alternative model of an accretion powered jet following the direct collapse of a massive star to a black hole. Contextual filtering of alert streams combined with rapid photometric verification using multiband imaging provides an efficient way to identify future members of this class, even at high redshift., LG was funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 839090. This work has been partially supported by the Spanish grant PGC2018-095317-B-C21 within the European Funds for Regional Development (FEDER). LG acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2019 Ramón y Cajal program RYC2019-027683 and from the Spanish MICIU project PID2020-115253GA-I00. HK thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant #1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. ECK acknowledges support from the GREAT research environment funded by Vetenskapsrådet, the Swedish Research Council, under project number 2016-06012, and support from The Wenner-Gren Foundations. MN is supported by a Royal Astronomical Society Research Fellowship. MG is supported by the Polish NCN MAESTRO grant 2014/14/A/ST9/00121. T-WC acknowledges the EU Funding under Marie Skłodowska-Curie grant H2020-MSCA-IF-2018-842471.

The discovery, characterisation, and monitoring of Near-Earth Objects (NEOs) are critical for understanding and potentially mitigating the long-term threats to our civilisation from Potential Hazardous Asteroids (PHAs). Current survey telescopes have a sensitivity of around 20–21 magnitude, which means PHAs, with absolute magnitude H > 22, are typically discovered at distances of a fraction of an astronomical unit (Jedicke et al. 2016). This has two consequences: first, the angular speeds of these objects are often tens of arc-seconds per minute in discovery data, smearing out the faintest objects and making the discovery even more challenging. Second, uncertainties in preliminary orbits calculated from discovery data coupled with the relatively short distance from Earth lead to large uncertainties in the sky positions of these objects: ranging from tens of arc-seconds to a fraction of a degree just half a day after discovery. To confirm such faint objects and refine their orbits, one needs meter class telescopes with relatively wide fields of view. GROWTH-India Telescope (GIT1, MPC Observatory Code: N51) is a 70-cm robotic telescope located at the Indian Astronomical Observatory (IAO) site at Hanle, Ladakh. Equipped with a 4k back-illuminated CCD, GIT has a 0.7° field of view at 0.67" resolution and reaches a depth of r' ≈ 21 in 5-minute exposures. GIT was set up as part of the Global Relay of Observatories Watching Transients Happen (Kasliwal et al. 2019)2, an international collaboration with NEO studies as one of its key science goals. GIT began solar system observations in September 2020 and has been used to observe 75 solar system objects as of May 2021 (Figure 1). GIT is broadly used for three types of solar system studies. First, we study NEOs to confirm the discoveries and refine their orbits. The geographic location of GIT — on the opposite side of Earth to the major NEO discovery engines like ZTF (Bellm et al. 2018), CSS (Christensen et al. 2018), ATLAS (Tonry et al. 2018) and PanSTARRs (Chambers et al. 2016) — allows us to observe NEOs before the positional uncertainties blow up to unmanageable scales. Secondly, we undertake coordinated observations of solar system objects with other observatories to obtain continuous coverage over long time spans. An excellent example is the joint study of the episodically active asteroid (6478) Gault (Purdum et al. 2021) where continuous observations were key to reveal the 2.5-hour rotational period. Lastly, we also undertake observations of cometary outbursts - 29P/Schwassmann-Wachmann 1 (Kelley et al. 2021d), 22P/Kopff (Kelley et al. 2021a), C/2020 R4 (ATLAS) (Kelley et al. 2021b) and 99P/Kowal 1 (Kelley et al. 2021c). Calculating accurate asteroid positions and magnitudes from non-sidereally tracked images poses a unique challenge. All the star images appear as streaks, and standard astrometry software are ill-suited for detecting and extracting such elongated sources. A common approach is to use the start (end) point of each streak as markers for the star positions at the start (end) of the exposure. But this approach needs significant human intervention. We have developed a new automated pipeline to process such images and obtain asteroid positions and photometry. Our pipeline detects streaks in the image and creates a synthetic image with point-like sources that can be solved for astrometry with any software. The final astrometric solutions can be transferred back to the original image, giving a coordinate system for the mid-point of observations. Testing our pipeline on sources with angular speeds as high as 2'/min and stellar streaks up to 5' in length, we have consistently obtained asteroid positions with arc-second residuals (Figure 2). This pipeline is built using open-source python packages like photutils (Bradley et al. 2020), and will soon be released publicly. The GROWTH-India Telescope (GIT), set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay with support from the Indo-US Science and Technology Forum (IUSSTF) and the Science and Engineering Research Board (SERB) of the Department of Science and Technology (DST), Government of India. It is located at IAO (Hanle), operated by IIA. Figure 1: An (a, e, i) orbital distribution of all solar system objects observed with GIT, including 36 NEOs, 15 Main-Belt Asteroids (MBAs), 1 Jupiter Trojan, 7 Periodic Comets and 16 Non-Periodic Comets. The region between perihelion q = 1.3 AU and aphelion Q = 0.983 AU demarcates the NEO regime. We have observed 5 Atens (NEOs with Q ≥ 0.983 AU and a < 1 AU), 21 Apollos (NEOs with a ≥ 1 AU and q ≤ 1.0167 AU) and 9 Amors (NEOs with 1.0167 AU < q ≤ 1.3 AU). The orbital parameters of periodic comets with a > 4 AU and non-periodic comets are not included in this figure. We have also observed 5 Inner MBAs (a ≤ 2.5 AU and q ≥ 1.66 AU), 5 Central MBAs (2.5 < a ≤ 2.8 AU and q ≥ 1.66 AU) and 7 Outer MBAs (a > 2.8 AU and q ≥ 1.66 AU). Figure 2. Observed-minus-Computed (O-C) residuals in the X and Y directions of all positions of NEOs observed with GIT. The NEOs tracked had a proper motion in the range of 4 − 120"/min. The exposures of 40 − 500 s were taken, resulting in streaking reference stars of lengths in the range 22 − 310". Astrometry on this data was performed using the GROWTH-India Astrometry Pipeline with a standard deviation of 0.57", which is fairly good for faint and fast-moving NEOs. References: Eric C. Bellm et al 2019 PASP 131 018002 Bradley, L. et al. 2020, Zenodo, doi: 10.5281/zenodo.4049061 Chambers, K. C. et al. 2016, arXiv e-prints, arXiv:1612.05560 Christensen, E. et al. 2018, AAS Vol. 50, Abstracts #50, 310.10 Jedicke, R. et al. 2016, Icarus, 266, 173 Kasliwal, M. M. et al. 2019, PASP, 131, 038003 Kelley, M. S. P. et al. 2021a, ATel, 14565, 1 -. 2021b, ATel, 14618, 1 -. 2021c, ATel, 14628, 1 -. 2021d, ATel, 14543, 1 Purdum, J. N. et al. 2021, ApJL, 911, L35 Tonry, J. L. et al. 2018, PASP, 130, 064505 1https://sites.google.com/view/growthindia/ 2https://www.growth.caltech.edu/

Malin 1, being a class of giant low surface galaxies, continues to surprise us even today. The HST/F814W observation has shown that the central region of Malin 1 is more like a normal SB0/a galaxy, while the rest of the disk has the characteristic of a low surface brightness system. The AstroSat/UVIT observations suggest scattered recent star formation activity all over the disk, especially along the spiral arms. The central 9" ($\sim 14$ kpc) region, similar to the size of the Milky Way's stellar disk, has a number of far-UV clumps - indicating recent star-formation activity. The high resolution UVIT/F154W image reveals far-UV emission within the bar region ($\sim 4$ kpc) - suggesting the presence of hot, young stars in the bar. These young stars from the bar region are perhaps responsible for producing the strong emission lines such as H$\alpha$, [OII] seen in the SDSS spectra. Malin 1B, a dwarf early-type galaxy, is interacting with the central region and probably responsible for inducing the recent star-formation activity in this galaxy., Comment: 15 pages, 10 figures, accepted for publication in the Journal of Astrophysics and Astronomy

We report the discovery of a nearby large, diffuse galaxy that shows star formation, using Ultra Violet Imaging Telescope (UVIT) far-UV observations, archival optical data from Multi-Unit Spectroscopic Explorer (MUSE) and Dark Energy Camera Legacy Survey (DECaLS), and InfraRed Survey Facility (IRSF) near-infrared observations. The galaxy was not detected earlier due to its superposition with the background galaxy, NGC 6902A. They were together mistakenly classified as an interacting system. NGC 6902A is at a redshift of 0.05554, but MUSE observations indicate that the interacting tail is a separate star-forming, foreground galaxy at a redshift of 0.00980. We refer to the new galaxy as UVIT J202258.73-441623.8 (UVIT J2022). The near-infrared observations show that UVIT J2022 has a stellar mass of 8.7$\times$10$^{8}$M$_{\odot}$. Its inner disk (R$, Comment: 6 pages, 4 figures, Accepted in A&A Letters

All authors: Kasliwal, Mansi M.; Anand, Shreya; Ahumada, Tomás; Stein, Robert; Carracedo, Ana Sagués; Andreoni, Igor; Coughlin, Michael W.; Singer, Leo P.; Kool, Erik C.; De, Kishalay; Kumar, Harsh; AlMualla, Mouza; Yao, Yuhan; Bulla, Mattia; Dobie, Dougal; Reusch, Simeon; Perley, Daniel A.; Cenko, S. Bradley; Bhalerao, Varun; Kaplan, David L.; Sollerman, Jesper; Goobar, Ariel; Copperwheat, Christopher M.; Bellm, Eric C.; Anupama, G. C.; Corsi, Alessandra; Nissanke, Samaya; Agudo, Iván; Bagdasaryan, Ashot; Barway, Sudhanshu; Belicki, Justin; Bloom, Joshua S.; Bolin, Bryce; Buckley, David A. H.; Burdge, Kevin B.; Burruss, Rick; Caballero-García, Maria D.; Cannella, Chris; Castro-Tirado, Alberto J.; Cook, David O.; Cooke, Jeff; Cunningham, Virginia; Dahiwale, Aishwarya; Deshmukh, Kunal; Dichiara, Simone; Duev, Dmitry A.; Dutta, Anirban; Feeney, Michael; Franckowiak, Anna; Frederick, Sara; Fremling, Christoffer; Gal-Yam, Avishay; Gatkine, Pradip; Ghosh, Shaon; Goldstein, Daniel A.; Golkhou, V. Zach; Graham, Matthew J.; Graham, Melissa L.; Hankins, Matthew J.; Helou, George; Hu, Youdong; Ip, Wing-Huen; Jaodand, Amruta; Karambelkar, Viraj; Kong, Albert K. H.; Kowalski, Marek; Khandagale, Maitreya; Kulkarni, S. R.; Kumar, Brajesh; Laher, Russ R.; Li, K. L.; Mahabal, Ashish; Masci, Frank J.; Miller, Adam A.; Mogotsi, Moses; Mohite, Siddharth; Mooley, Kunal; Mroz, Przemek; Newman, Jeffrey A.; Ngeow, Chow-Choong; Oates, Samantha R.; Patil, Atharva Sunil; Pandey, Shashi B.; Pavana, M.; Pian, Elena; Riddle, Reed; Sánchez-Ramírez, Rubén; Sharma, Yashvi; Singh, Avinash; Smith, Roger; Soumagnac, Maayane T.; Taggart, Kirsty; Tan, Hanjie; Tzanidakis, Anastasios; Troja, Eleonora; Valeev, Azamat F.; Walters, Richard; Waratkar, Gaurav; Webb, Sara; Yu, Po-Chieh; Zhang, Bin-Bin; Zhou, Rongpu; Zolkower, Jeffry, We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo's third observing run (O3). We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook follow-up with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization area of 4480 deg2, a median distance of 267 Mpc, and false-alarm rates ranging from 1.5 to 10-25 yr-1. The ZTF coverage in the g and r bands had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. The O3 follow-up by the GROWTH team comprised 340 UltraViolet/Optical/InfraRed (UVOIR) photometric points, 64 OIR spectra, and three radio images using 17 different telescopes. We find no promising kilonovae (radioactivity-powered counterparts), and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. Initially, we assume that all GW triggers are bona fide astrophysical events regardless of false-alarm rate and that kilonovae accompanying BNS and NSBH mergers are drawn from a common population; later, we relax these assumptions. Assuming that all kilonovae are at least as luminous as the discovery magnitude of GW170817 (-16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than-16.6 mag (the extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag day-1 (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations based on the online classifications, the joint probability of zero detections, assuming all kilonovae are brighter than-16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than 10-4, or φ > 30° to be consistent with our limits. We look forward to searches in the fourth GW observing run; even 17 neutron star mergers with only 50% coverage to a depth of-16 mag would constrain the maximum fraction of bright kilonovae to, This work was supported by the Global Relay of Observatories Watching Transients Happen (GROWTH) project, funded by the National Science Foundation under PIRE grant No. 1545949. GROWTH is a collaborative project among the California Institute of Technology (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK), and University of Sydney (Australia). Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. The ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. The ZTF forced photometry service was funded under Heising-Simons Foundation grant No. 12540303 (PI: Graham). The SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171. The GROWTH-India telescope is a 70 cm telescope with a 0.7 degrees field of view, set up by the Indian Institute of Astrophysics and the Indian Institute of Technology Bombay with support from the Indo-US Science and Technology Forum (IUSSTF) and the Science and Engineering Research Board (SERB) of the Department of Science and Technology (DST), Government of India (https://sites.google.com/view/growthindia/). It is located at the Indian Astronomical Observatory (Hanle), operated by the Indian Institute of Astrophysics (IIA). The GROWTH-India project is supported by SERB and administered by IUSSTF under grant No. IUSSTF/PIRE Program/GROWTH/2015-16. This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France (doi: 10.26093/cds/vizier). The original description of the VizieR service was published in A&AS 143, 23. These results made use of the Lowell Discovery Telescope (LDT) at Lowell Observatory. Lowell is a private, nonprofit institution dedicated to astrophysical research and public appreciation of astronomy and operates the LDT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University, and Yale University. The Large Monolithic Imager was built by Lowell Observatory using funds provided by the National Science Foundation (AST-1005313). The upgrade of the DeVeny optical spectrograph has been funded by a generous grant from John and Ginger Giovale and a grant from the Mt. Cuba Astronomical Foundation. The KPED team thanks the National Science Foundation and the National Optical Astronomical Observatory for making the Kitt Peak 2.1 m telescope available. We thank the observatory staff at Kitt Peak for their efforts to assist Robo-AO KP operations. The KPED team thanks the National Science Foundation, the National Optical Astronomical Observatory, the Caltech Space Innovation Council, and the Murty family for support in the building and operation of KPED. In addition, they thank the CHIMERA project for use of the Electron Multiplying CCD (EMCCD). The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Some spectroscopic observations were obtained with the Southern African Large Telescope (SALT). The Photometric Redshifts for the Legacy Surveys (PRLS) catalog used in this paper was produced thanks to funding from the U.S. Department of Energy Office of Science, Office of High Energy Physics, via grant DE-SC0007914. This publication has made use of data collected at Lulin Observatory, partly supported by MoST grant 108-2112-M-008-001. Based on observations made with the Gran Telescopio Canarias (GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias on the island of La Palma. M.M.K. acknowledges generous support from the David and Lucille Packard Foundation. M.W.C. acknowledges support from the National Science Foundation with grant No. PHY-2010970. A.G. and J.S. acknowledge support from the Knut and Alice Wallenberg Foundation and GREAT research environment grant 2016-06012, funded by the Swedish Research Council. Some of the work by D.A.P. was performed at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. D.A.P. was partially supported by a grant from the Simons Foundation. H.K. thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant 1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. This work has been supported by the Spanish Science Ministry Centro de Excelencia Severo Ochoa Program under grant SEV-2017-0709. A.J.C.T. acknowledges support from the Junta de Andalucia (Project P07-TIC-03094) and Spanish Ministry Projects AYA2012-39727-C03-01, AYA2015-71718R, and PID-019-109974RB-I00. V.A.F. was supported by grant RFBR 19-02-00432. I.A. acknowledges support by a Ramon y Cajal grant (RYC-2013-14511) of the Ministerio de Ciencia, Innovacion, y Universidades (MICIU) of Spain. He also acknowledges financial support from MCIU through grant AYA2016-80889-P. A.A.M. is funded by the Large Synoptic Survey Telescope Corporation, the Brinson Foundation, and the Moore Foundation in support of the LSSTC Data Science Fellowship Program; he also receives support as a CIERA Fellow by the CIERA Postdoctoral Fellowship Program (Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University). A.C. acknowledges support from the National Science Foundation with grant No. 1907975. W.-H.I., A. K., K.-L.L., C.-C.N., A.P., H.T., and P.-C.Y. acknowledge support from Ministry of Science and Technology (MoST) Taiwan grants 104-2923-M-008-004-MY5, 107-2119-M-008-012, 108-2628-M-007-005-RSP, and 108-2112-M-007-025-MY3. D.D. is supported by an Australian Government Research Training Program Scholarship. S.A. is supported by the GROWTH project, funded by the National Science Foundation under PIRE grant No. 1545949. A.S.C. is supported by GREAT research environment grant 2016-06012, funded by the Swedish Research Council. E.C.K. acknowledges support from the G.R.E.A.T. research environment and the Wenner-Gren Foundations. A.J.C.T. is thankful for fruitful discussions with J. Cepa, E. Fernandez-Garcia, J. A. Font, S. Jeong, A. Martin-Carrillo, A. M. Sintes, and S. Sokolov. D.A.H.B. acknowledges research support from the National Research Foundation of South Africa. S.B.P. and V.B. acknowledge BRICS grant No. "DST/IMRCD/BRICS/PilotCall1/ProFCheap/2017(G)" for part of the present work. J.S.B. was partially supported by a Gordon and Betty Moore Foundation Data-Driven Discovery grant and a grant from the National Science Foundation, "Conceptualization of a Scalable Cyberinfrastructure Center for Multimessenger Astrophysics."

We report the discovery of a bar, a pseudobulge and unresolved point source in the archetype collisional ring galaxy Cartwheel using careful morphological analysis of a near-infrared (NIR) K$_s$ band image of excellent quality (seeing=0.42\arcsec) at the ESO archive. The bar is oval-shaped with a semi-major axis length of 3.23\arcsec\($\sim$2.09~kpc), with almost a flat light distribution along it. The bulge is almost round (ellipticity=0.21) with an effective radius of 1.62\arcsec\ ($\sim$1.05~kpc) and a Sersic index of 0.99, parameters typical of pseudobulges in late-type galaxies. The newly discovered bar is not recognisable as such in the optical images even with more than a factor of two higher spatial resolution of the Hubble Space Telescope, due to a combination of its red colour and the presence of dusty features. The observed bar and pseudobulge most likely belonged to the pre-collisional progenitor of the Cartwheel. The discovery of a bar in an archetype collisional ring galaxy Cartwheel is the first observational evidence to confirm the prediction that bars can survive a drop-through collision along with the morphological structures like a central bulge (pseudo)., Comment: Accepted for publication in MNRAS, 8 pages, 3 figures, 2 tables

Based on the colour measurements from a multi-band, multi-component 2D decomposition's of S0 and spiral galaxies using SDSS images, we found that bars are bluer in S0 galaxies compared to the spiral galaxies. Most of the S0s in our sample have stellar masses $\sim L_{*}$ galaxies. The environment might have played an important role as most of the S0s with bluer bars are in the intermediate-density environment. The possibility of minor mergers and tidal interactions which occurs frequently in the intermediate-density environment might have caused either a bar to form and/or induce star formation in the barred region of S0 galaxies. The underlying discs show the usual behaviour being redder in S0s compared to spiral galaxies while the bulges are red and old for both S0 and spiral galaxies. The finding of bluer bars in S0 galaxies is a puzzling issue and poses an interesting question at numerical and theoretical studies most of which shows that the bars are long-lived structures with old stellar populations., Comment: 10 pages, 7 figures, accepted for publication in MNRAS

In this paper, we try to understand why the classical bulge fraction observed in S0 galaxies is significantly higher than that in spiral galaxies. We carry out a comparative study of the bulge and global properties of a sample of spiral and S0 galaxies in a fixed environment. Our sample is flux limited and contains 262 spiral and 155 S0 galaxies drawn from the Sloan Digital Sky Survey. We have classified bulges into classical and pseudobulge categories based on their position on the Kormendy diagram. Dividing our sample into bins of galaxy stellar mass, we find that the fraction of S0 galaxies hosting a classical bulge is significantly higher than the classical bulge fraction seen in spirals even at fixed stellar mass. We have compared the bulge and the global properties of spirals and S0 galaxies in our sample and find indications that spiral galaxies which host a classical bulge, preferentially get converted into S0 population as compared to pseudobulge hosting spirals. By studying the star formation properties of our galaxies in the NUV-r color-mass diagram, we find that the pseudobulge hosting spirals are mostly star forming while the majority of classical bulge host spirals are in the green valley or in the passive sequence. We suggest that some internal process, such as AGN feedback or morphological quenching due to the massive bulge, quenches these classical bulge hosting spirals and transforms them into S0 galaxies, thus resulting in the observed predominance of the classical bulge in S0 galaxies., Comment: 8 pages, 3 figures, accepted for publication in MNRAS

We monitored the comet 67P/Churyumov-Gerasimenko close to its perihelion in November 2021 with the GROWTH-India Telescope. We observed two outbursts of this comet on 2021 October 29.940 and November 17.864 UTC, −3.12 days and +15.81 days respectively from the perihelion date. The brightening in the first outburst appears as a compact source, with a radial extent up to 8.″5. The comet brightened by 0.26 ± 0.03 mag in the outburst, with a 27% increase in the effective geometric cross-section and total outburst dust mass of ∼5.3 × 105 kg. The second outburst caused a brightening of 0.49 ± 0.08 mag with effective geometric cross-section and total outburst dust mass 2.5 times larger than the first event. These outbursts are up to an order of magnitude larger than the strongest outburst event observed in situ by the Rosetta spacecraft in 2015.

Context. Galaxy interactions and mergers can lead to supermassive black hole (SMBH) binaries, which become active galactic nucleus (AGN) pairs when the SMBHs start accreting mass. If there is a third galaxy involved in the interaction, then a triple-AGN system can form. Aims. Our goal is to investigate the nature of the nuclear emission from the galaxies in the interacting pair NGC 7733–NGC 7734 using archival VLT/MUSE integral field spectrograph data and study its relation to the stellar mass distribution traced by near-infrared (NIR) observations from the South African Astronomical Observatory (SAAO). Methods. We conducted NIR observations using the SAAO and identified the morphological properties of bulges in each galaxy. We used MUSE data to obtain a set of ionized emission lines from each galaxy and studied the ionization mechanism. We also examined the relation of the galaxy pair with any nearby companions with far-ultraviolet observations using the UVIT. Results. The emission line analysis from the central regions of NGC 7733 and NGC 7734 shows Seyfert and low ionization nuclear emission-line regions type AGN activity. The galaxy pair NGC 7733−34 also shows evidence of a third component, which has Seyfert-like emission. Hence, the galaxy pair NGC 7733−34 forms a triple-AGN system. We also detected an extended narrow-line region associated with the nucleus of NGC 7733.

We present evidence for bimodal stellar age distribution of pseudobulges of S0 galaxies as probed by the $D_n(4000)$ index. We do not observe any bimodality in age distribution for pseudobulges in spiral galaxies. Our sample is flux limited and contains 2067 S0 and 2630 spiral galaxies drawn from the Sloan Digital Sky Survey. We identify pseudobulges in S0 and spiral galaxies, based on the position of the bulge on the Kormendy diagram and their central velocity dispersion. Dividing the pseudobulges of S0 galaxies into those containing old and young stellar populations, we study the connection between global star formation and pseudobulge age on the $u-r$ color-mass diagram. We find that most old pseudobulges are hosted by passive galaxies while majority of young bulges are hosted by galaxies which are star forming. Dividing our sample of S0 galaxies into early-type S0s and S0/a galaxies, we find that old pseudobulges are mainly hosted by early-type S0 galaxies while most of the pseudobulges in S0/a galaxies are young. We speculate that morphology plays a strong role in quenching of star formation in the disc of these S0 galaxies, which stops the growth of pseudobulges, giving rise to old pseudobulges and the observed age bimodality., Comment: 6 pages, 3 figures, Accepted for publication in MNRAS Letters

Using multi-wavelength data, from UV-optical-near-mid IR, for $\sim$6000 galaxies in the local Universe, we study the dependence of star formation on the morphological T-types for massive galaxies ($\log M_*/M_\odot \geq 10$). We find that, early-type spirals (Sa-Sbc) and S0s predominate in the green valley, which is a transition zone between the star forming and quenched regions. Within the early-type spirals, as we move from Sa to Sbc spirals the fraction of green valley and quenched galaxies decreases, indicating the important role of the bulge in the quenching of galaxies. The fraction of early-type spirals decreases as we enter the green valley from the blue cloud, which coincides with the increase in the fraction of S0s. This points towards the morphological transformation of early-type spiral galaxies into S0s which can happen due to environmental effects such as ram-pressure stripping, galaxy harassment, or tidal interactions. We also find a second population of S0s which are actively star-forming and are present in all environments. Since morphological T-type, specific star formation rate (sSFR), and environmental density are all correlated with each other, we compute the partial correlation coefficient for each pair of parameters while keeping the third parameter as a control variable. We find that morphology most strongly correlates with sSFR, independent of the environment, while the other two correlations (morphology-density and sSFR-environment) are weaker. Thus, we conclude that, for massive galaxies in the local Universe, the physical processes that shape their morphology are also the ones that determine their star-forming state., 18 pages, 15 figures, and 9 tables. Accepted for publication in MNRAS

Here we report the discovery with the Giant Metrewave Radio Telescope of an extremely large ($\sim$115 kpc in diameter) HI ring off-centered from a massive quenched galaxy, AGC 203001. This ring does not have any bright extended optical counterpart, unlike several other known ring galaxies. Our deep $g$, $r$, and $i$ optical imaging of the HI ring, using the MegaCam instrument on the Canada-France-Hawaii Telescope, however, shows several regions with faint optical emission at a surface brightness level of $\sim$28 mag/arcsec$^2$. Such an extended HI structure is very rare with only one other case known so far -- the Leo ring. Conventionally, off-centered rings have been explained by a collision with an "intruder" galaxy leading to expanding density waves of gas and stars in the form of a ring. However, in such a scenario the impact also leads to large amounts of star formation in the ring which is not observed in the ring presented in this paper. We discuss possible scenarios for the formation of such HI dominated rings., Accepted for publication in MNRAS, 7 pages, 5 figures and 2 tables

In this work, we investigate the reason behind the increased occurrence of S0 galaxies in high density environments. Our sample comprises of $\sim$ 2500 spiral and $\sim$ 2000 S0 galaxies spanning a wide range of environments. Dividing the galaxies into categories of classical and pseudobulge hosting spiral and S0 galaxies, we have studied their properties as a function of the environment. We find that the fraction of pseudobulge hosting disc galaxies decreases with increase in density. The classical bulge hosting spirals and S0 galaxies follow a similar trend in less dense environments but towards higher densities, we observe an increase in the fraction of classical bulge host S0 galaxies at the expense of spirals. Comparing the structural and the star formation properties of galaxies on the size-mass and $NUV-r$ colour-mass planes respectively, we infer that classical bulge hosting spirals are likely to get transformed into S0 morphology. We notice a trend of galaxy structure with environment such that the fraction of classical bulge hosting spiral galaxies is found to increase with environment density. We also find that among classical bulge hosting spirals, the fraction of quenched galaxies increases in denser environments. We surmise that the existence of more classical bulge hosting spirals galaxies and more efficient quenching leads to the observed increased occurrence of S0 galaxies in high density environments. The relation between galaxy structure and environment also exists for the disc galaxies irrespective of their visual morphology, which is driven mainly by halo mass., Comment: 14 pages, 8 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

Star formation in galaxies is a hierarchical process with a wide range of scales from smaller clusters to larger stellar complexes. Here, we present an ultra-violet imaging study of the nearby flocculent spiral galaxy NGC 7793, observed with the Ultra-Violet Imaging Telescope (UVIT). We find that the disk scale-length estimated in Far-UV (2.64$\pm$0.16 kpc) is larger than that in Near-UV (2.21$\pm$0.21 kpc) and optical (1.08 kpc), which supports the inside-out growth scenario of the galaxy disk. The star-forming UV disk is also found to be contained within the extent of H~I gas of column density greater than $10^{21}$cm$^{-2}$. With the spatial resolution of UVIT (1 pixel $\sim$ 6.8 pc), we identified 2046 young star-forming clumps in the galaxy with radii between $\sim$ 12 - 70 pc, which matches well with the size of GMCs detected in the galaxy. Around 61\% of the regions identified in our study have age younger than 20 Myr, which points to a recent enhancement of star formation across the galaxy. We also noticed that the youngest star-forming regions, with age $, Comment: 17 pages, 14 figures, Accepted for publication in ApJ

Earlier studies have shown that massive bulges impede bar formation in disk galaxies. Recent N-body simulations have derived a bar formation criterion that depends on the radial bulge force in a galaxy disk. We use those simulations to show that bars can form only when the force constant FB < 0.13, where FB depends on the ratio of the bulge force to the total force of the galaxy at twice the disk scale length 2R d . In this article, we test this theoretical prediction using observational data obtained from the literature. Our sample consists of 63 barred galaxies with a wide range of Hubble classes from the S 4 G catalogue for which bulge, disk and bar decomposition has been done. We find that 92 % of our sample galaxies satisfy the condition FB < 0.13 for bar formation in galaxies and hence agree with the bar formation criterion given by the simulations., 7 pages, 5 figures, accepted for publication in A&A

We present observations of pseudobulges in S0 and spiral galaxies using imaging data taken with the Spitzer Infra-Red Array Camera. We have used 2-d bulge-disk-bar decomposition to determine structural parameters of 185 S0 galaxies and 31 nearby spiral galaxies. Using the Sersic index and the position on the Kormendy diagram to classify their bulges as either classical or pseudo, we find that 25 S0s (14%) and 24 spirals (77%) host pseudoblges. The fraction of pseudobulges we find in spiral galaxies is consistent with previous results obtained with optical data and show that the evolution of a large fraction of spirals is governed by secular processes rather than by major mergers. We find that the bulge effective radius is correlated with the disk scale length for pseudobulges of S0s and spirals, as expected for secular formation of bulges from disk instabilities, though the disks in S0s are significantly smaller than those in spirals. We show that early-type pseudobulge hosting spirals can transform to pseudobulge hosting S0s by simple gas stripping. However, simple gas stripping mechanism is not sufficient to transform the late-type pseudobulge hosting spirals into pseudobulge hosting S0s., 12 pages, 7 figures, accepted for publication in MNRAS

We perform a $z$-band survey for an optical counterpart of a binary neutron star coalescence GW170817 with Subaru/Hyper Suprime-Cam. Our untargeted transient search covers $23.6$ deg$^2$ corresponding to the $56.6\%$ credible region of GW170817 and reaches the $50\%$ completeness magnitude of $20.6$ mag on average. As a result, we find 60 candidates of extragalactic transients, including J-GEM17btc (a.k.a. SSS17a/DLT17ck). While J-GEM17btc is associated with NGC 4993 that is firmly located inside the 3D skymap of GW170817, the other 59 candidates do not have distance information in the GLADE v2 catalog or NASA/IPAC Extragalactic Database (NED). Among 59 candidates, 58 are located at the center of extended objects in the Pan-STARRS1 catalog, while one candidate has an offset. We present location, $z$-band apparent magnitude, and time variability of the candidates and evaluate the probabilities that they are located inside of the 3D skymap of GW170817. The probability for J-GEM17btc is $64\%$ being much higher than those for the other 59 candidates ($9.3\times10^{-3}-2.1\times10^{-1}\%$). Furthermore, the possibility, that at least one of the other 59 candidates is located within the 3D skymap, is only $3.2\%$. Therefore, we conclude that J-GEM17btc is the most-likely and distinguished candidate as the optical counterpart of GW170817., 14 pages, 9 figures. Accepted for publication in PASJ (Publications of the Astronomical Society of Japan)

We report on SALT low resolution optical spectroscopy and optical/IR photometry undertaken with other SAAO telescopes (MASTER-SAAO and IRSF) of the kilonova AT 2017gfo (aka SSS17a) in the galaxy NGC4993 during the first 10 days of discovery. This event has been identified as the first ever electromagnetic counterpart of a gravitational wave event, namely GW170817, which was detected by the LIGO and Virgo gravitational wave observatories. The event is likely due to a merger of two neutron stars, resulting in a kilonova explosion. SALT was the third telescope to obtain spectroscopy of AT 2017gfo and the first spectrum, 1.2 d after the merger, is quite blue and shows some broad features, but no identifiable spectral lines and becomes redder over time. We compare the spectral and photometric evolution with recent kilonova simulations and conclude that they are in qualitative agreement for post-merger wind models with proton: nucleon ratios of $Y_e$ = 0.25$-$0.30. The blue colour of the first spectrum is consistent with the lower opacity of the Lathanide-free r-process elements in the ejecta. Differences between the models and observations are likely due to the choice of system parameters combined with the absence of atomic data for more elements in the ejecta models., 5 pages, 4 figures, 1 table

Only one carbon-rich (C-rich, hereinafter) Mira variable has so far been suggested as a member of the Galactic bulge and this is in a symbiotic system. Here we describe a method for selecting C-rich candidates from an infrared colour-colour diagram, (J-Ks) vs ([9]-[18]). Follow-up low-resolution spectroscopy resulted in the detection of 8 C-rich Mira variables from a sample of36 candidates towards the Galactic bulge. Our near-infrared photometry indicates that two of these, including the known symbiotic, are closer than the main body of the bulge while a third is a known foreground object. Of the 5 bulge members, one shows He I and [O II] emission and is possibly another symbiotic star. Our method is useful for identifying rare C-rich stars in the Galactic bulge and elsewhere. The age of these C-rich stars and the evolutionary process which produced them remain uncertain. They could be old and the products of either binary mass transfer or mergers, i.e. the descendants of blue stragglers, but we cannot rule out the possibility that they belong to a small in-situ population of metal-poor intermediate age (less than 5 Gyr) stars in the bulge or that they have been accreted from a dwarf galaxy., 9 pages, 8 figures, 2 tables, accepted for publication in MNRAS

The first detected gravitational wave from a neutron star merger was GW170817. In this study, we present J-GEM follow-up observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5-mag decline in the $z$-band from 1.7 days to 7.7 days after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder for later epochs; the $z-H$ color changed by approximately 2.5 mag in the period of 0.7 days to 7.7 days. The rapid evolution of both the optical brightness and the color are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized $r$-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that $r$-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with the ejecta mass of 0.01 $\Msun$, which suggests a more intense mass ejection ($\sim 0.03 \Msun$) or possibly an additional energy source., Comment: 7 pages, 5 figures. Published in PASJ (Publications of the Astronomical Society of Japan)

We examine the dependence of the fraction of galaxies containing pseudo bulges on environment for a flux limited sample of $\sim$5000 SDSS galaxies. We have separated bulges into classical and pseudo bulge categories based on their position on the Kormendy diagram. Pseudo bulges are thought to be formed by internal processes and are a result of secular evolution in galaxies. We attempt to understand the dependence of secular evolution on environment and morphology. Dividing our sample of disc+bulge galaxies based on group membership into three categories: central and satellite galaxies in groups and isolated field galaxies, we find that pseudo bulge fraction is almost equal for satellite and field galaxies. Fraction of pseudo bulge hosts in central galaxies is almost half of the fraction of pseudo bulges in satellite and field galaxies. This trend is also valid when only galaxies are considered only spirals or S0. Using the projected fifth nearest neighbour density as measure of local environment, we look for the dependence of pseudo bulge fraction on environmental density. Satellite and field galaxies show very weak or no dependence of pseudo bulge fraction on environment. However, fraction of pseudo bulges hosted by central galaxies decreases with increase in local environmental density. We do not find any dependence of pseudo bulge luminosity on environment. Our results suggest that the processes that differentiate the bulge types are a function of environment while processes responsible for the formation of pseudo bulges seem to be independent of environment., Comment: 8 pages, 7 figures, to appear in the MNRAS

We have discovered a population of 29 outlying Hα emitters which appear like unresolved blobs in the DR14 data release of the SDSS IV MaNGA integral field unit survey. They do not have any underlying optical continuum emission in deep imaging from the DECam Legacy Survey or Beijing-Arizona Sky Survey. These blobs either lie away from the disc of the host galaxy in the MaNGA IFU and/or have velocities which are different from the velocity map of the host galaxy. Interestingly, all of them show photoionisation due to star formation. These galaxies have very high specific star formation rates compared to the known population of dwarf galaxies. However, their metallicities are consistent with or even lowerthan those of the local volume dwarfs. Thus, we can possibly rule out tidal dwarf galaxies. They could represent a new population of low mass and starbursting dwarf galaxies.

High cadence ultraviolet, optical and near-infrared photometric and low-resolution spectroscopic observations of the peculiar Type II supernova (SN) 2018hna are presented. The early phase multiband light curves exhibit the adiabatic cooling envelope emission following the shock breakout up to ~14 days from the explosion. SN~2018hna has a rise time of $\sim$\,88 days in the V-band, similar to SN 1987A. A $\rm^{56}Ni$ mass of ~0.087$\pm$0.004 $\rm M_{\odot}$ is inferred for SN 2018hna from its bolometric light curve. Hydrodynamical modelling of the cooling phase suggests a progenitor with a radius ~50 $\rm R_{\odot}$, a mass of ~14-20 $\rm M_{\odot}$ and explosion energy of ~1.7-2.9$\rm \times$ $\rm 10^{51}\ erg$. The smaller inferred radius of the progenitor than a standard red supergiant is indicative of a blue supergiant progenitor of SN 2018hna. A sub-solar metallicity (~0.3 $\rm Z_{\odot}$) is inferred for the host galaxy UGC 07534, concurrent with the low-metallicity environments of 1987A-like events., 8 pages, 5 figures, Accepted for Publication in ApJ Letters

We combine UV/Optical/near-IR/mid-IR data on a sample of ~240 S0 galaxies to examine various star formation related processes in them. We split the sample into bright and faint S0 galaxies based on their K band luminosity. Comparing the FUV-NUV versus NUV-K color-color diagram with a Simple Stellar Population (SSP) model shows that ellipticals and bright S0 galaxies are dominated by a stellar population of age > 10^9 years while faint S0 galaxies may contain stars as young as 10^8 years, providing evidence for relatively recent star formation activity. The strength of the 4000A break is also systematically higher in brighter S0 galaxies, again indicating the presence of an old stellar population. Their mid-IR colours indicate that bright S0 colours are like those of ellipticals while faint S0 colours are more like spirals. All these observations are consistent with a scenario in which low-luminosity S0 galaxies likely formed by the stripping of gas from the discs of late-type spiral galaxies, which in turn formed their pseudo bulges through secular evolution processes, possibly involving multiple episodes of star formation. On the other hand, more luminous S0 galaxies likely formed the bulk of their stars at early epochs, similar to the star formation in elliptical galaxies, and are characterised by an old coeval stellar population and classical bulge, Accepted for publication in MNRAS: 9 pages, 8 figures

S0 galaxies are known to host classical bulges with a broad range of size and mass, while some such S0s are barred and some not. The origin of the bars has remained as a long-standing problem -- what made bar formation possible in certain S0s? By analysing a large sample of S0s with classical bulges observed by the Spitzer space telescope, we find that most of our barred S0s host comparatively low-mass classical bulges, typically with bulge-to-total ratio ($B/T$) less than $0.5$; whereas S0s with more massive classical bulges than these do not host any bar. Furthermore, we find that amongst the barred S0s, there is a trend for the longer and massive bars to be associated with comparatively bigger and massive classical bulges -- possibly suggesting bar growth being facilitated by these classical bulges. In addition, we find that the bulge effective radius is always less than the bar effective radius --indicating an interesting synergy between the host classical bulge and bars being maintained while bar growth occurred in these S0s., Accepted for publication in MNRAS Letters: 5 pages, 4 figures

We present results from an on-going programme to study the dust and ionized gas in E/S0 galaxies with dust lanes. Our data, together with results from previous studies of E/S0 galaxies, are used to demonstrate the tight relationship between these two components. This relationship is discussed in light of our current understanding of the nature and origin of the interstellar medium (ISM), and in particular in the context of the interplay between the different multi-temperature components. We show that focusing on dust obscured regions as tracers of the ISM, and on their properties, serves as independent evidence for the external origin of the dust and ionized gas.

We present new high-speed, multi-observatory, multi-instrument photometry of the eclipsing polar UZ For in order to measure precise mid-eclipse times with the aim of detecting any orbital period variations. When combined with published eclipse times and archival data spanning ~27 years, we detect departures from a linear and quadratic trend of ~60 s. The departures are strongly suggestive of two cyclic variations of 16(3) and 5.25(25) years. The two favoured mechanisms to drive the periodicities are either two giant extrasolar planets as companions to the binary (with minimum masses of 6.3(1.5)M(Jupiter) and 7.7(1.2)M(Jupiter)) or a magnetic cycle mechanism (e.g. Applegate's mechanism) of the secondary star. Applegate's mechanism would require the entire radiant energy output of the secondary and would therefore seem to be the least likely of the two, barring any further refinements in the effect of magnetic fieilds (e.g. those of Lanza et al.). The two planet model can provide realistic solutions but it does not quite capture all of the eclipse times measurements. A highly eccentric orbit for the outer planet would fit the data nicely, but we find that such a solution would be unstable. It is also possible that the periodicities are driven by some combination of both mechanisms. Further observations of this system are encouraged.

We present a study of bars in lenticular galaxies based on a sample of 371 galaxies from the SDSS-DR 7 and 2MASS in optical and near-infrared bands, respectively. We found a bar in 15% of the lenticular galaxies in our sample, which is consistent with recent studies. The barred galaxy fraction shows a luminosity dependence, with faint lenticular galaxies (MK > -24.5, total absolute magnitude in K band) having a larger fraction of bars than bright lenticular galaxies (MK < -24.5). A similar trend is seen when Mr = -21.5, the total absolute magnitude in SDSS r band is used to divide the sample into faint and bright lenticular galaxies. We find that faint galaxies in clusters show a higher bar fraction than their counterparts in the field. This suggests that the formation of bars in lenticular galaxies not only depends on the total luminosity of galaxy but also on the environment of the host galaxy.

We study the photometric parameters of the bulges of galaxies of different Hubble types including ellipticals, lenticulars, early and late type spirals and early type dwarf galaxies. Analyzing the distributions of various photometric parameters, and two- and three-dimensional correlations between them, we find that there is a difference in the correlations exhibited by bright (M_K < -22) and faint bulges, irrespective of their Hubble type. Importantly, the bright bulges, which include typically E/S0 galaxies and bulges of early type spirals, are tightly distributed around a common photometric plane (PP), while their fainter counter parts, mainly bulges of late type spirals and dwarf galaxies show significant deviation from the planar distribution. We show that the specific entropy, determined from the bulge structural parameters, systematically increases as we move from late to early Hubble types. We interpret this as evidence for hierarchical merging and passive evolution scenarios for bright and faint bulges respectively., 27 pages, 16 figures, accepted in A&A

We present multicolor surface and aperture photometry in the B, V, R, and K' bands for a sample of 34 lenticular galaxies from the Uppsala General Catalogue. From surface photometric analysis, we obtain radial profiles of surface brightness, colors, ellipticity, position angle, and the Fourier coefficients that describe the departure of isophotal shapes from a purely elliptical form; we find the presence of dust lanes, patches, and ringlike structure in several galaxies in the sample. We obtain total integrated magnitudes and colors and find that these are in good agreement with the values from the Third Reference Catalogue. Isophotal colors are correlated with each other, following the sequence expected for early-type galaxies. The color gradients in lenticular galaxies are more negative than the corresponding gradients in elliptical galaxies. There is a good correlation between B-V and B-R color gradients, and the mean gradients in the B-V, B-R, and V-K' colors are -0.13 ± 0.06, -0.18 ± 0.06, and -0.25 ± 0.11 mag dex -1 in radius, respectively.

An analysis of the star cluster population in a low-luminosity early type galaxy, NGC 2328, is presented. The clusters are found in a tight star-forming nuclear spiral/ring pattern and we also identify a bar from structural 2D decomposition. These massive clusters are forming very efficiently in the circum-nuclear environment, they are young, possibly all less than 30 Myr of age. The clusters indicate an azimuthal age gradient, consistent with a "pearls-on-a-string" formation scenario suggesting bar driven gas inflow. The cluster mass function has a robust down-turn at low masses at all age bins. Assuming clusters are born with a power-law distribution, this indicates extremely rapid disruption at time-scales of just several Myr. If found to be typical, it means that clusters born in dense circum-nuclear rings do not survive to become old globular clusters in non-interacting systems., Comment: Accepted to ApJ Letters. 5 pages using emulateapj

Nova Sco 2008 was recently shown to have resulted from the merger of the two stars in the contact binary V1309 Sco. This is the first stellar merger ever observed between two convective stars. We present archival data, new infrared photometry, and Hubble Space Telescope WFC3 imaging of V1309 Sco. Spitzer observations show that it had a large infrared excess in the 3.6 μm to 8 μm range more than a year before the merger. Standard color diagnostics of the pre-merger infrared colors place V1309 Sco in the same region where evolved stars with chemically complex mass loss are located. Since the nova outburst subsided in optical bandpasses in 2008, the merger remnant's brightness in optical bandpasses, near-IR bandpasses, and the Spitzer 3.6 μm and 4.5 μm channels has varied by several magnitudes and in complex ways. A temporary, strong increase in the reddening during 2010 suggests the occurrence of a dust formation event. We point out several peculiarities in the relative fluxes and time behavior of the optical and near-IR magnitudes, which could be explained if some of the photometric bandpasses in the 1-5 μm range are strongly affected by emission lines.

A comparison of pseudobulges in S0 and spiral galaxies is presented using structural parameters derived from 2-d decomposition of mid-infrared images taken at 3.6 μm by Spitzer IRAC. The position of the bulges on the Kormendy diagram has been used as an initial classification criterion for determining the nature of the bulge. To make the classification more secure, the criterion proposed by Fisher and Drory (2008) has also been used, which involves using the n = 2 division line on Sérsic index. We find that among the 185 S0 galaxies, 27 are pseudobulge hosts while 160 are classical. Of these 25 pseudobulge hosts, only two belong to the bright luminosity class (MK < 22.66, AB system) while rest belong to the faint luminosity class (MK > 22.66, AB system). We find that among spiral galaxies, 77 % (24 of 31) of the bulges are classified as pseudobulges. As pointed out by various studies, the presence of such a large fraction poses problems to our current picture of galaxy formation. How ever, our primary result is that the disk scale length of pseudobulge hosting S0s is significantly smaller on average than that of their spiral counterparts. This can be explained as a lowered disk luminosity which in turn implies that S0s have evolved from spiral progenitors. We also argue that early type spirals are more likely to be the progenitors based on bulge and total luminosity arguments. We speculate that if late type spirals hosting pseudobulges have to evolve into S0s, an additional mechanism along with gas stripping of spirals is needed. We have also investigated the effect of environment on pseudobulges in the two samples, but no significant trends were found in the properties of the pseudobulges as a function of the various structural parameters. The study is made more difficult because of the low number statistics one deals with when the sample is sub-divided based on whether it is in a field or group/cluster environment. The study of pseudobulges based on environment, however, is an interesting one and is something that can be considered for the future by carefully selecting a sample with statistically meaningful number of objects from diverse environments.

We consider the luminosity and environmental dependence of structural parameters of lenticular galaxies in the near-infrared K band. Using a two-dimensional galaxy image decomposition technique, we extract bulge and disk structural parameters for a sample of 36 lenticular galaxies observed by us in the K band. By combining data from the literature for field and cluster lenticulars with our data, we study correlations between parameters that characterise the bulge and the disk as a function of luminosity and environment. We find that scaling relations such as the Kormendy relation, photometric plane and other correlations involving bulge and disk parameters show a luminosity dependence. This dependence can be explained in terms of galaxy formation models in which faint lenticulars (M_T > -24.5) formed via secular formation processes that likely formed the pseudobulges of late-type disk galaxies, while brighter lenticulars (M_T < -24.5) formed through a different formation mechanism most likely involving major mergers. On probing variations in lenticular properties as a function of environment, we find that faint cluster lenticulars show systematic differences with respect to faint field lenticulars. These differences support the idea that the bulge and disk components fade after the galaxy falls into a cluster, while simultaneously undergoing a transformation from spiral to lenticular morphologies., Published in MNRAS; added correct Bibliographic reference; 10 pages, 2 tables and 11 figures

We obtain the coefficients of a new fundamental plane for supermassive black holes at the centers of elliptical galaxies, involving measured central black hole mass and photometric parameters which define the light distribution. The galaxies are tightly distributed around this mass fundamental plane, with improvement in the rms residual over those obtained from the $\mbh-\sigma$ and $\mbh-L$ relations. This implies a strong multidimensional link between the central massive black hole formation and global photometric properties of elliptical galaxies and provides an improved estimate of black hole mass from galaxy data., Comment: Accepted for publication in ApJ Letters

We investigate the correlation between the bulge effective radius (r_e) and disk scale length (r_d), in the near-infrared K band for lenticular galaxies in the field and in clusters. We find markedly different relations between the two parameters as a function of luminosity. Lenticulars with total absolute magnitude fainter than M_T = -24.5 show a positive correlation, in line with predictions of secular formation processes for the pseudo bulges of late-type disk galaxies. But brighter lenticulars with M_T < -24.5 show an anti-correlation, indicating that they formed through a different mechanism. The available data are insufficient to reliably determine the effect of galaxy environment on this correlation., Accepted for publication in ApJ Letters, 4 pages, 3 figures; minor typos are corrected

(Abridged) Luminous Compact Galaxies (LCGs) (M_B < -20, R_{1/2} < 4.5kpc and EW_{0}(OII) >15��) constitute one of the most rapidly evolving galaxy populations over the last ~8 Gyr history of the universe. Due to their inherently compact sizes, any detailed quantitative analysis of their morphologies has proved to be difficult in the past. In this work we use the high angular resolution imaging data, from the HST/ACS GOODS survey, to study the quantitative morphology of a complete sample of LCGs in the redshift range 0.5 < z < 1.2. We have derived structural parameters for a representative sample of 39 LCGs selected from the GOODS-S field, using full 2-dimensional surface brightness profile fitting of the galaxy images in each of the four filters available. B-z color maps are used as an aid in the morphological classification. We then use the rest frame B band bulge flux fraction (B/T) to determine the morphological class of the galaxies. Mergers were essentially identified visually by the presence of multiple maxima of comparable intensity in the rest frame B band images, aided by the color maps to distinguish them from HII regions. We derive the following morphological mix for our sample of intermediate redshift LCGs: Mergers: ~36%, Disk dominated: ~22%, S0: ~20%, Early types: ~7%, Irr/tadpole: ~15%. We establish that our sample LCGs are intermediate mass objects with a median stellar mass of Log(M/M_{\odot})=10.32. We also derive dust enshrouded SFR values ranging from a few to ~65 $M_{\odot}$/year using Spitzer 24$��m$ data. We estimate a factor ~11 fall in the comoving number density of blue LCGs from redshifts 0.5 < z < 1.2 to the current epoch. We finally discuss the evolutionary scenario of these LCGs which might give us some clues regarding their descendants in the local universe., Accepted for publication in A&A. 24 Pages, 10 figures. Fits files of sample galaxies available at http://www.iucaa.ernet.in/~rawat/lcg_1.html