Search

We present the integral field spectroscopic observations of ionized gas (H$\alpha$ and [{\ion{N}{II}}]) using the PCWI, along with deep CO(2-1) observations by the $^\backprime\bar{\rm U}^\backprime\bar{\rm u}$ receiver on JCMT for AGC 102004. The velocity field of H$\alpha$ shows an anomalous distribution in the North-Western (NW) disk. The H$\alpha$ spectrum is well-fitted by two Gaussian components, and the weak Gaussian component is dominated by the anomalous H$\alpha$ in the NW disk. The Gaussian fit center of H$\alpha$ emission is offset by +24.2 km s$^{-1}$ from the systemic velocity obtained from the HI emission. We derive the gas-phase metallicity, 12+log(O/H), using [{\ion{N}{II}}]$\lambda$6583/H$\alpha$ ratio as a proxy. The mean value of 12+log(O/H) is 8.30 $\pm$ 0.19 over the whole galaxy. The metallicity in the outer disk is lower than the detection limit of 7.72, indicating the metallicity gradient exists in AGC 102004. We speculate a minor/mini-merger event could have happened to the NW disk. CO(2-1) emission has non-detection in AGC 102004, reaching a noise level of 0.33 mK smoothed to 30 km s$^{-1}$. The upper limit of molecular gas mass in AGC 102004 is 2.1 $\times$ 10$^7$ M$\odot$ with X$_{\rm CO}$ = 3.02$\times$10$^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$. The M$_{\rm H_2}$/M$^{\rm corr}_{\rm HI}$ of AGC 102004 is lower than 0.0037 and lower than that of normal galaxies., Comment: 10 pages, 9 figures, Accepted for publication in ApJ

Aims. The central region of the Giant Low Surface Brightness galaxy Malin 1 has long been known to have a complex morphology with evidence of a bulge, disc, and potentially a bar hosting asymmetric star formation. In this work, we use VLT/MUSE data to resolve the central region of Malin 1 in order to determine its structure. Methods. We use careful light profile fitting in every image slice of the datacube to create wavelength-dependent models of each morphological component, from which we could cleanly extract their spectra. We then used the kinematics and emission line properties from these spectra to better understand the nature of each component extracted from our model fit. Results. We report the detection of a pair of distinct sources at the centre of this galaxy with a separation of ~1.05", which corresponds to a separation on sky of ~1.9 kpc. The radial velocity data of each object confirms that they both lie in the kinematic core of the galaxy, and analysis of the emission lines reveals that the central compact source is more consistent with being ionized by star formation and/or a LINER, while the off-centre compact source lies closer to the separation between star-forming galaxies and AGN. Conclusions. This evidence suggests that the centre of Malin 1 hosts either a bar with asymmetric star formation or two distinct components in which the off-centre compact source could either be a star-forming clump containing one or more star clusters that is in the process of falling into the core of the galaxy and which will eventually merge with the central NSC, or a clump of gas infalling into the centre of the galaxy from either outside or from the disc and triggering star formation there., Comment: 13 pages, 5 figures, accepted for publication in A&A

The detection of gravitational waves from a binary neutron star merger by Advanced LIGO and Advanced Virgo (GW170817), along with the discovery of the electromagnetic counterparts of this gravitational wave event, ushered in a new era of multimessenger astronomy, providing the first direct evidence that BNS mergers are progenitors of short gamma-ray bursts (GRBs). Such events may also produce very-high-energy (VHE, > 100GeV) photons which have yet to be detected in coincidence with a gravitational wave signal. The Cherenkov Telescope Array (CTA) is a next-generation VHE observatory which aims to be indispensable in this search, with an unparalleled sensitivity and ability to slew anywhere on the sky within a few tens of seconds. New observing modes and follow-up strategies are being developed for CTA to rapidly cover localization areas of gravitational wave events that are typically larger than the CTA field of view. This work will evaluate and provide estimations on the expected number of of gravitational wave events that will be observable with CTA, considering both on- and off-axis emission. In addition, we will present and discuss the prospects of potential follow-up strategies with CTA., Comment: Presented at the 38th International Cosmic Ray Conference (ICRC 2023), 2023 (arXiv:2309.08219)

Large-scale asymmetries (i.e. lopsidedness) are a common feature in the stellar density distribution of nearby disk galaxies both in low- and high-density environments. In this work, we characterize the present-day lopsidedness in a sample of 1435 disk-like galaxies selected from the TNG50 simulation. We find that the percentage of lopsided galaxies (10%-30%) is in good agreement with observations if we use similar radial ranges to the observations. However, the percentage (58%) significantly increases if we extend our measurement to larger radii. We find a mild or lack of correlation between lopsidedness amplitude and environment at z=0 and a strong correlation between lopsidedness and galaxy morphology regardless of the environment. Present-day galaxies with more extended disks, flatter inner galactic regions and lower central stellar mass density (i.e. late-type disk galaxies) are typically more lopsided than galaxies with smaller disks, rounder inner galactic regions and higher central stellar mass density (i.e. early-type disk galaxies). Interestingly, we find that lopsided galaxies have, on average, a very distinct star formation history within the last 10 Gyr, with respect to their symmetric counterparts. Symmetric galaxies have typically assembled at early times (~8-6 Gyr ago) with relatively short and intense bursts of central star formation, while lopsided galaxies have assembled on longer timescales and with milder initial bursts of star formation, continuing building up their mass until z=0. Overall, these results indicate that lopsidedness in present-day disk galaxies is connected to the specific evolutionary histories of the galaxies that shaped their distinct internal properties., Comment: Submitted to MNRAS, 23 pages (including the Appendix), 23 figures

We present a sample of 330 blue edge-on low surface brightness galaxies (ELSBGs). To understand the chemical evolution of LSBGs, we derived the gas-phase abundance and the [$\alpha$/Fe] ratio. Compared with star-forming galaxies, ELSBGs show a flatter trend in the mass-metallicity ($M_*-Z$) relation, suggesting that the oxygen abundance enhancement is inefficient. We focus on 77 ELSBGs with HI data and found the closed-box model can not explain their gas fraction and metallicity relation, implying that infall and/or outflow is needed. We derived the [$\alpha$/Fe] ratio of normal ELSBG ($<$ 10$^{9.5}$M$\odot$) and massive ELSBG ($>=$ 10$^{9.5}$M$\odot$) using single stellar population grids from MILES stellar library. The mean [$\alpha$/Fe] ratios are 0.18 and 0.4 for normal ELSBG and massive ELSBG, respectively. We discussed that the long time-scale of star-formation, and/or metal-rich gas outflow event caused by SNe Ia winds are likely responsible for the $\alpha$-enhancement of massive ELSBGs., Comment: 9 pages, 9 figures, Accepted for publication in ApJ

We report on results from GBT/ARGUS $^{12}$CO(1-0) observations for the giant low surface brightness galaxy Malin 1, which allow us to determine an upper limit for its CO mass, and hence its molecular gas mass and molecular gas mass surface density $\Sigma_{H_2}$. Although we performed very deep observations through 17 hours on source integration time, reaching a noise level of $\sim 0.2$ mK (T$^{*}_{A}$) with a corresponding extended source CO limit (3$\sigma$) of 0.09 K km s$^{-1}$, 19 times more sensitive than previous works, we do not detect the $^{12}$CO(1-0) emission line. However, the observations allow us to estimate an upper limit (3$\sigma$) for the CO mass of about $7.4 \times 10^9$ M$_\odot$ for the extended emission, and $1.4 \times 10^8$ M$_\odot$ for the central part of the galaxy. With these figures we conclude that the molecular gas surface density is lower than 0.3 M$_\odot$ pc$^{-2}$, and the corresponding molecular to atomic gas mass ratio is lower than 0.13. The evidence suggests a quite different physical conditions for the interstellar medium in Malin 1 compared to that of normal, high surface brightness spirals. This, in one way to another, keeps an usual molecular gas tracer as CO hidden from our observations, in spite of the diverse stellar and structural properties of Malin 1 observed by several authors since more than 30 years., Comment: This is the final (proof-corrected) version, published in ApJ Letters

Rare giant low surface brightness galaxies (gLSBGs) act as a stress test for the current galaxy formation paradigm. To answer the question `How rare are they?' we estimate their volume density in the local Universe. A visual inspection of 120~sq.~deg. covered by deep Subaru Hyper Suprime-Cam data was performed independently by four team members. We detected 42 giant disky systems (30 of them isolated) at $z\leq0.1$ with either $g$-band 27.7~mag~arcsec$^{-2}$ isophotal radius or four disc scalelengths $4h \geq 50$~kpc, 37 of which (including 25 isolated) had low central surface brightness ($\mu_{0,g}\ge 22.7$ mag~arcsec$^{-2}$). This corresponds to volume densities of 4.70$\times 10^{-5}$ Mpc$^{-3}$ for all galaxies with giant extended discs and 4.04$\times 10^{-5}$ Mpc$^{-3}$ for gLSBGs, which converts to $\sim $12,700 such galaxies in the entire sky out to $z<0.1$. These estimates agree well with the result of the EAGLE cosmological hydrodynamical simulation. Giant disky galaxies represent the large-size end of the volume density distribution of normal-sized spirals, suggesting the non-exceptional nature of giant discs. We observe a high active galactic nucleus fraction among the newly found gLSBGs., Comment: 5 pages, 2 tables, 5 figures, accepted for publication in MNRAS Letters

Many processes have been proposed to explain the quenching of star formation in spiral galaxies and their transformation into S0s. These processes affect the bulge and disc in different ways, and so by isolating the bulge and disc spectra, we can look for these characteristic signatures. In this work, we used BUDDI to cleanly extract the spectra of the bulges and discs of 78 S0 galaxies in the MaNGA Survey. We compared the luminosity and mass weighted stellar populations of the bulges and discs, finding that bulges are generally older and more metal rich than their discs. When considering the mass and environment of each galaxy, we found that the galaxy stellar mass plays a more significant role on the formation of the bulges. Bulges in galaxies with masses $\geq10^{10}M_\odot$ built up the majority of their mass rapidly early in their lifetimes, while those in lower mass galaxies formed over more extended timescales and more recently. No clear difference was found in the formation or quenching processes of the discs as a function of galaxy environment. We conclude that more massive S0 galaxies formed through an inside-out scenario, where the bulge formed first and evolved passively while the disc underwent a more extended period of star formation. In lower mass S0s, the bulges and discs either formed together from the same material, or through an outside-in scenario. Our results therefore imply multiple formation mechanisms for S0 galaxies, the pathway of which is chiefly determined by a galaxy's current stellar mass., Comment: 17 pages, 12 figures, accepted for publication in MNRAS

Using observed data from the literature, we compare in one single publication the angular momentum (AM) of low surface brightness galaxies (LSBGs), with that of high surface brightness galaxies (HSBGs), a comparison that either is currently spread across many unconnected references, or simply does not exist. Partly because of the subject, this has received little attention outside the realm of simulations. We use previous results of the stellar specific AM $j_{*}$ from the SPARC database containing Spitzer 3.6 $\mu$m photometry and accurate H I rotation curves from Lelli et al. using a sample of 38 LSBGs and 82 HSBGs. We do this with the objective of comparing both galaxy populations, finding that LSBGs are higher in the Fall relation by about 0.174 dex. Additionally, we apply and test different masses and formation models to estimate the spin parameter $\lambda$, which quantifies the rotation obtained from the tidal torque theory, finding no clear evidence of a difference in the spin of LSBGs and HSBGs under a classic disk formation model that assumes the ratio ($f_{j}$) between $j_{*}$ and the specific AM of the halo is $\sim 1$. In another respect, by using the biased collapse model, where $f_{j}$ depends on the star formation efficiency, it was found that LSBGs clearly show higher spin values, having an average spin of $\sim 2$ times the average spin of HSBGs. This latter result is consistent with those obtained from simulations by Dalcanton et al., Comment: 13 pages, 10 figures

We present a new measurement of the Ly$\alpha$ luminosity function at redshift $z=6.9$, finding moderate evolution from $z=5.7$ that is consistent with a fully or largely ionized $z\sim7$ intergalactic medium. Our result is based on four fields of the LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) project. Our survey volume of $6.1\times10^{6}$ Mpc$^{3}$ is double that of the next largest $z\sim 7$ survey. We combine two new LAGER fields (WIDE12 and GAMA15A) with two previously reported LAGER fields (COSMOS and CDFS). In the new fields, we identify $N=95$ new $z=6.9$ Ly$\alpha$ emitters (LAEs); characterize our survey's completeness and reliability; and compute Ly$\alpha$ luminosity functions. The best-fit Schechter luminosity function parameters for all four LAGER fields are in good general agreement. Two fields (COSMOS and WIDE12) show evidence for a bright-end excess above the Schechter function fit. We find that the Ly$\alpha$ luminosity density declines at the same rate as the UV continuum LF from $z=5.7$ to $z=6.9$. This is consistent with an intergalactic medium that was fully ionized as early as redshift $z\sim 7$, or with a volume-averaged neutral hydrogen fraction of $x_{HI} < 0.33$ at $1\sigma$., Comment: 19 pages, 11 figures; accepted by ApJ

Protoclusters, the progenitors of the most massive structures in the Universe, have been identified at redshifts of up to 6.6. Besides exploring early structure formation, searching for protoclusters at even higher redshifts is particularly useful to probe the reionization. Here we report the discovery of the protocluster LAGER-z7OD1 at a redshift of 6.93, when the Universe was only 770 million years old and could be experiencing rapid evolution of the neutral hydrogen fraction in the intergalactic medium. The protocluster is identified by an overdensity of 6 times the average galaxy density, and with 21 narrowband selected Lyman-$\alpha$ galaxies, among which 16 have been spectroscopically confirmed. At redshifts similar to or above this record, smaller protogroups with fewer members have been reported. LAGER-z7OD1 shows an elongated shape and consists of two subprotoclusters, which would have merged into one massive cluster with a present-day mass of $3.7 \times 10^{15}$ solar masses. The total volume of the ionized bubbles generated by its member galaxies is found to be comparable to the volume of the protocluster itself, indicating that we are witnessing the merging of the individual bubbles and that the intergalactic medium within the protocluster is almost fully ionized. LAGER-z7OD1 thus provides a unique natural laboratory to investigate the reionization process., Comment: 9 pages, 5 figures, and 1 table. Accepted by Nature Astronomy

We investigate the on-average properties for 28 star-forming ultra-diffuse galaxies (UDGs) located in low-density environments, by stacking their spectra from the Sloan Digital Sky Survey. These relatively-isolated UDGs, with stellar masses of $\log_{10}(M_*/M_{\odot})\sim 8.57\pm0.29$, have the on-average total-stellar-metallicity [M/H]$\sim -0.82\pm0.14$, iron-metallicity [Fe/H]$\sim -1.00\pm0.16$, stellar age $t_*\sim5.2\pm0.5$ Gyr, $\alpha$-enhancement [$\alpha$/Fe]$\sim 0.24\pm0.10$, and oxygen abundance 12+log(O/H)$\sim 8.16\pm0.06$, as well as central stellar velocity dispersion $54\pm12$ km/s. On the star-formation rate versus stellar mass diagram, these UDGs are located lower than the extrapolated star-forming main sequence from the massive spirals, but roughly follow the main sequence of low-surface-brightness dwarf galaxies. We find that these star-forming UDGs are not particularly metal-poor or metal-rich for their stellar masses, as compared with the metallicity-mass relations of the nearby typical dwarfs. With the UDG data of this work and previous studies, we also find a coarse correlation between [Fe/H] and magnesium-element enhancement [Mg/Fe] for UDGs: [Mg/Fe]$\simeq-0.43(\pm0.26)$[Fe/H]$-0.14(\pm0.40)$., Comment: Accepted for publication in ApJL

Clues to the formation and evolution of Nuclear Star Clusters (NSCs) lie in their stellar populations. However, these structures are often very faint compared to their host galaxy, and spectroscopic analysis of NSCs is hampered by contamination of light from the rest of the system. With the introduction of wide-field IFU spectrographs, new techniques have been developed to model the light from different components within galaxies, making it possible to cleanly extract the spectra of the NSCs and study their properties with minimal contamination from the light of the rest of the galaxy. This work presents the analysis of the NSCs in a sample of 12 dwarf galaxies in the Fornax Cluster observed with MUSE. Analysis of the stellar populations and star-formation histories reveal that all the NSCs show evidence of multiple episodes of star formation, indicating that they have built up their mass further since their initial formation. The NSCs were found to have systematically lower metallicities than their host galaxies, which is consistent with a scenario for mass-assembly through mergers with infalling globular clusters, while the presence of younger stellar populations and gas emission in the core of two galaxies is indicative of in-situ star formation. We conclude that the NSCs in these dwarf galaxies likely originated as globular clusters that migrated to the core of the galaxy which have built up their mass mainly through mergers with other infalling clusters, with gas-inflow leading to in-situ star formation playing a secondary role., Comment: 18 pages, 13 figures. Accepted for publication in MNRAS

The 8.4m Vera Rubin Observatory Legacy Survey of Space and Time (LSST) will start a ten-year survey of the southern hemisphere sky in 2023. LSST will revolutionise low surface brightness astronomy. It will transform our understanding of galaxy evolution, through the study of low surface brightness features around galaxies (faint shells, tidal tails, halos and stellar streams), discovery of low surface brightness galaxies and the first set of statistical measurements of the intracluster light over a significant range of cluster masses and redshifts., Comment: Invited talk, to appear in the Proceedings of the IAU Symposium 355, 'The Realm of the Low-surface-brightness Universe'

We investigate the formation and properties of low surface brightness galaxies (LSBGs) with $M_{*} > 10^{9.5} \mathrm{M_{\odot}}$ in the EAGLE hydrodynamical cosmological simulation. Galaxy surface brightness depends on a combination of stellar mass surface density and mass-to-light ratio ($M/L$), such that low surface brightness is strongly correlated with both galaxy angular momentum (low surface density) and low specific star formation rate (high $M/L$). This drives most of the other observed correlations between surface brightness and galaxy properties, such as the fact that most LSBGs have low metallicity. We find that LSBGs are more isolated than high surface brightness galaxies (HSBGs), in agreement with observations, but that this trend is driven entirely by the fact that LSBGs are unlikely to be close-in satellites. The majority of LSBGs are consistent with a formation scenario in which the galaxies with the highest angular momentum are those that formed most of their stars recently from a gas reservoir co-rotating with a high-spin dark matter halo. However, the most extended LSBG disks in EAGLE, which are comparable in size to observed giant LSBGs, are built up via mergers. These galaxies are found to inhabit dark matter halos with a higher spin in their inner regions ($<0.1r_{200c}$), even when excluding the effects of baryonic physics by considering matching halos from a dark matter only simulation with identical initial conditions., Comment: Version accepted to MNRAS. 20 pages, 13 figures, plus appendix with 2 figures

Using the photometric data from the Next Generation Fornax Survey, we find a significant radial alignment signal among the Fornax dwarf galaxies. For the first time, we report that the radial alignment signal of nucleated dwarfs is stronger than that of non-nucleated ones at 2.4$\sigma$ confidence level, and the dwarfs located in the outer region ($R>R_{\rm{vir}}/3$; $R_{\rm{vir}}$ is the Fornax virial radius) show slightly stronger radial alignment signal than those in the inner region ($R

With the published data of apparent axis ratios for 1109 ultra-diffuse galaxies (UDGs) located in 17 low-redshift (z~ 0.020 - 0.063) galaxy clusters and 84 UDGs in 2 intermediate-redshift (z~ 0.308 - 0.348) clusters, we take advantage of a Markov Chain Monte Carlo approach and assume a ubiquitous triaxial model to investigate the intrinsic morphologies of UDGs. In contrast to the conclusion of Burkert (2017), i.e., the underlying shapes of UDGs are purely prolate ($C=B

The Large Synoptic Survey Telescope (LSST) can advance scientific frontiers beyond its groundbreaking 10-year survey. Here we explore opportunities for extended operations with proposal-based observing strategies, new filters, or transformed instrumentation. We recommend the development of a mid-decade community- and science-driven process to define next-generation LSST capabilities., Comment: Astro2020 APC White Paper, 8 pages, 1 figure

We present the largest-ever sample of 79 Ly$\alpha$ emitters (LAEs) at $z\sim$ 7.0 selected in the COSMOS and CDFS fields of the LAGER project (the Lyman Alpha Galaxies in the Epoch of Reionization). Our newly amassed ultradeep narrowband exposure and deeper/wider broadband images have more than doubled the number of LAEs in COSMOS, and we have selected 30 LAEs in the second field CDFS. We detect two large-scale LAE-overdense regions in the COSMOS that are likely protoclusters at the highest redshift to date. We perform injection and recovery simulations to derive the sample incompleteness. We show significant incompleteness comes from blending with foreground sources, which however has not been corrected in LAE luminosity functions in {the} literature. The bright end bump in the Ly$\alpha$ luminosity function in COSMOS is confirmed with 6 (2 newly selected) luminous LAEs (L$_{Ly\alpha}$ $>$ 10$^{43.3}$ erg s$^{-1}$). Interestingly, the bump is absent in CDFS, in which only one luminous LAE is detected. Meanwhile, the faint end luminosity functions from the two fields well agree with each other. The 6 luminous LAEs in COSMOS coincide with 2 LAE-overdense regions, while such regions are not seen in CDFS. The bright-end luminosity function bump could be attributed to ionized bubbles in a patchy reionization. It appears associated with cosmic overdensities, thus supports an inside-out reionization topology at $z$ $\sim$ 7.0, i.e., the high density peaks were ionized earlier compared to the voids. An average neutral hydrogen fraction of $x_{HI}$ $\sim$ 0.2 -- 0.4 is derived at $z\sim$ 7.0 based on the cosmic evolution of the Ly$\alpha$ luminosity function., Comment: 23 pages, 11 figures, 2 tables, accepted for publication in ApJ

We present the design for the first narrowband filter NB964 for the Dark Energy Camera (DECam), which is operated on the 4m Blanco Telescope at the Cerro Tololo Inter-American Observatory. The NB964 filter profile is essentially defined by maximizing the power of searching for Lyman alpha emitting galaxies (LAEs) in the epoch of reionization, with the consideration of the night sky background in the near-infrared and the DECam quantum efficiency. The NB964 filter was manufactured by Materion in 2015. It has a central wavelength of 964.2 nm and a full width at half maximum (FWHM) of 9.2 nm. An NB964 survey named LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) has been ongoing since December 2015. Here we report results of lab tests, on-site tests and observations with the NB964 filter. The excellent performances of this filter ensure that the LAGER project is able to detect LAEs at z~7 with a high efficiency., Comment: 12 pages, 12 figures, submitted to PASP

We report the detection of a pair of dwarf galaxies at $z\!=\!0.30$ which may be in the early stages of an interaction. Both galaxies have stellar masses of $<10^{9}M_\odot$, and display a projected separation of $\sim\!29$kpc and a physical separation of $\sim\!240$kpc. Evidence of ongoing star formation has been found in both galaxies, with neither one showing an enhanced star-formation rate that would be expected if they were already interacting. One galaxy displays a disturbed morphology but shows ordered gas rotation, which may reflect a previous minor merger event in the recent history of that system. The nearest spectroscopically confirmed neighbour lies at a distance of 38Mpc. These results indicate that these dwarf galaxies have no neighbouring massive galaxies, however with the data available we have been unable to determine whether these galaxies are isolated in the field or belong to a group of low-mass galaxies. As a detection of a rare dwarf-dwarf pair beyond the Local Universe, this system provides an uncommon opportunity to explore the properties of galaxy groups in the low-galaxy mass regime as a function of redshift., Comment: 16 pages, 8 figures, 1 table. Accepted for publication in ApJ. In version2 figure 8 was replaced to correct an error in the legend

We present a photometric study of the dwarf galaxy population in the core region ($< r_{\rm vir}/4$) of the Fornax galaxy cluster based on deep $u'g'i'$ photometry from the Next Generation Fornax Cluster Survey. All imaging data were obtained with the Dark Energy Camera mounted on the 4-meter Blanco telescope at the Cerro-Tololo Interamerican Observatory. We identify 258 dwarf galaxy candidates with luminosities $-17 < M_{g'} < -8$ mag, corresponding to typical stellar masses of $9.5\gtrsim \log{\cal M}_{\star}/M_\odot \gtrsim 5.5$, reaching $\sim\!3$ mag deeper in point-source luminosity and $\sim\!4$ mag deeper in surface-brightness sensitivity compared to the classic Fornax Cluster Catalog. Morphological analysis shows that surface-brightness profiles are well represented by single-component S\'ersic models with average S\'ersic indices of $\langle n\rangle_{u',g',i'}=(0.78-0.83) \pm 0.02$, and average effective radii of $\langle r_e\rangle_{u',g',i'}\!=(0.67-0.70) \pm 0.02$ kpc. Color-magnitude relations indicate a flattening of the galaxy red sequence at faint galaxy luminosities, similar to the one recently discovered in the Virgo cluster. A comparison with population synthesis models and the galaxy mass-metallicity relation reveals that the average faint dwarf galaxy is likely older than ~5 Gyr. We study galaxy scaling relations between stellar mass, effective radius, and stellar mass surface density over a stellar mass range covering six orders of magnitude. We find that over the sampled stellar mass range several distinct mechanisms of galaxy mass assembly can be identified: i) dwarf galaxies assemble mass inside the half-mass radius up to $\log{\cal M}_{\star}$ ~8.0, ii) isometric mass assembly in the range $8.0 < \log{\cal M}_{\star}/M_\odot < 10.5$, and iii) massive galaxies assemble stellar mass predominantly in their halos at $\log{\cal M}_{\star}$ ~10.5 and above., Comment: 19 pages, 9 figures, accepted for publication in ApJ

The Large Synoptic Survey Telescope (LSST) will enable revolutionary studies of galaxies, dark matter, and black holes over cosmic time. The LSST Galaxies Science Collaboration has identified a host of preparatory research tasks required to leverage fully the LSST dataset for extragalactic science beyond the study of dark energy. This Galaxies Science Roadmap provides a brief introduction to critical extragalactic science to be conducted ahead of LSST operations, and a detailed list of preparatory science tasks including the motivation, activities, and deliverables associated with each. The Galaxies Science Roadmap will serve as a guiding document for researchers interested in conducting extragalactic science in anticipation of the forthcoming LSST era., Comment: For more information, see https://galaxies.science.lsst.org

Narrowband imaging is a highly successful approach for finding large numbers of high redshift Lya emitting galaxies (LAEs) up to z~6.6. However, at z>~7 there are as yet only 3 narrowband selected LAEs with spectroscopic confirmations (two at z~6.9-7.0, one at z~7.3), which hinders extensive studies on cosmic reionization and galaxy evolution at this key epoch. We have selected 23 candidate z~6.9 LAEs in COSMOS field with the large area narrowband survey LAGER (Lyman-Alpha Galaxies at the End of Reionization). In this work we present spectroscopic followup observations of 12 candidates using IMACS on Magellan. For 9 of these, the observations are sufficiently deep to detect the expected lines. Lya emission lines are identified in six sources (yielding a success rate of 2/3), including 3 luminous LAEs with Lya luminosities of L(Lya) ~ 10^{43.5} erg/s, the highest among known spectroscopically confirmed galaxies at >~7.0. This triples the sample size of spectroscopically confirmed narrowband selected LAEs at z>~7, and confirms the bright end bump in the Lya luminosity function we previously derived based on the photometric sample, supporting a patchy reionization scenario. Two luminous LAEs appear physically linked with projected distance of 1.1 pMpc and velocity difference of ~ 170 km/s. They likely sit in a common ionized bubble produced by themselves or with close neighbors, which reduces the IGM attenuation of Lya. A tentative narrow NV${\lambda}$1240 line is seen in one source, hinting at activity of a central massive black hole with metal rich line emitting gas., Comment: 6 pages, 3 figures, 2 tables, accepted by ApJL

We present the first results from the ongoing LAGER project (Lyman Alpha Galaxies in the Epoch of Reionization), which is the largest narrowband survey for $z \sim$ 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m Blanco telescope, LAGER has collected 34 hours NB964 narrowband imaging data in the 3 deg$^2$ COSMOS field. We have identified 23 Lyman Alpha Emitter (LAE) candidates at $z$ = 6.9 in the central 2-deg$^2$ region, where DECam and public COSMOS multi-band images exist. The resulting luminosity function can be described as a Schechter function modified by a significant excess at the bright end (4 galaxies with $L_{Ly\alpha} \sim $ 10$^{43.4\pm0.2}$ erg s$^{-1}$). The number density at $L_{Ly\alpha}\sim$ 10$^{43.4\pm0.2}$ erg s$^{-1}$ is little changed from z= 6.6, while at fainter $L_{Ly\alpha}$ it is substantially reduced. Overall, we see a fourfold reduction in Ly$\alpha$ luminosity density from $z$ = 5.7 to 6.9. Combined with a more modest evolution of the continuum UV luminosity density, this suggests a factor of $\sim 3$ suppression of Ly$\alpha$ by radiative transfer through the $z \sim$ 7 intergalactic medium (IGM). It indicates an IGM neutral fraction $x_{HI}$ $\sim$ 0.4--0.6 (assuming Ly$\alpha$ velocity offsets of 100-200 km s$^{-1}$). The changing shape of the Ly$\alpha$ luminosity function between $z\lesssim 6.6$ and $z=6.9$ supports the hypothesis of ionized bubbles in a patchy reionization at $z\sim$ 7., Comment: 7 pages, 3 figures (updated), 2 tables (updated), Accepted for publication in ApJ Letters

We present Megacam deep optical images (g and r) of Malin 1 obtained with the 6.5m Magellan/Clay telescope, detecting structures down to ~ 28 B mag arcsec-2. In order to enhance galaxy features buried in the noise, we use a noise reduction filter based on the total generalized variation regularizator. This method allows us to detect and resolve very faint morphological features, including spiral arms, with a high visual contrast. For the first time, we can appreciate an optical image of Malin 1 and its morphology in full view. The images provide unprecedented detail, compared to those obtained in the past with photographic plates and CCD, including HST imaging. We detect two peculiar features in the disk/spiral arms. The analysis suggests that the first one is possibly a background galaxy, and the second is an apparent stream without a clear nature, but could be related to the claimed past interaction between Malin 1 and the galaxy SDSSJ123708.91 + 142253.2. Malin 1 exhibits features suggesting the presence of stellar associations, and clumps of molecular gas, not seen before with such a clarity. Using these images, we obtain a diameter for Malin 1 of 160 kpc, ~ 50 kpc larger than previous estimates. A simple analysis shows that the observed spiral arms reach very low luminosity and mass surface densities, to levels much lower than the corresponding values for the Milky Way., Comment: Accepted for publication in the Astrophysical Journal Letters (ApJ Letters), 3 Figures (reduced in size)

We present a compilation of UBV RIz light curves of 51 type II supernovae discovered during the course of four different surveys during 1986 to 2003: the Cerro Tololo Supernova Survey, the Calan/Tololo Supernova Program (C&T), the Supernova Optical and Infrared Survey (SOIRS), and the Carnegie Type II Supernova Survey (CATS). The photometry is based on template-subtracted images to eliminate any potential host galaxy light contamination, and calibrated from foreground stars. This work presents these photometric data, studies the color evolution using different bands, and explores the relation between the magnitude at maximum brightness and the brightness decline parameter (s) from maximum light through the end of the recombination phase. This parameter is found to be shallower for redder bands and appears to have the best correlation in the B band. In addition, it also correlates with the plateau duration, being thus shorter (longer) for larger (smaller) s values., Comment: 110 pages, 9 Figures, 6 Tables, accepted in AJ

We report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded $u, g$ and $i$-band image obtained with the DECam wide-field camera mounted on the 4-meter Blanco telescope at the Cerro Tololo Interamerican Observatory as part of the {\it Next Generation Fornax Survey} (NGFS). The new dwarf galaxies have quasi-exponential light profiles, effective radii $0.1\!<\!r_e\!<\!2.8$ kpc and average effective surface brightness values $22.0\!<\!\mu_i\!<\!28.0$ mag arcsec$^{-2}$. We confirm the existence of ultra-diffuse galaxies (UDGs) in the Fornax core regions that resemble counterparts recently discovered in the Virgo and Coma galaxy clusters.~We also find extremely low surface brightness NGFS dwarfs, which are several magnitudes fainter than the classical UDGs. The faintest dwarf candidate in our NGFS sample has an absolute magnitude of $M_i\!=\!-8.0$\,mag. The nucleation fraction of the NGFS dwarf galaxy sample appears to decrease as a function of their total luminosity, reaching from a nucleation fraction of $>\!75\%$ at luminosities brighter than $M_i\!\simeq\!-15.0$ mag to $0\%$ at luminosities fainter than $M_i\!\simeq\!-10.0$ mag. The two-point correlation function analysis of the NGFS dwarf sample shows an excess on length scales below $\sim\!100$ kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core., Comment: 6 pages, 3 figures. Accepted for publication in The Astrophysical Journal Letters. Download the high-resolution version of the paper from the following link: https://www.dropbox.com/s/xb9vz8s29wlzjgf/ms.pdf?dl=0

We mapped 3 mm continuum and line emission from the starburst galaxy M82 using the Combined Array for Research in Millimeter-wave Astronomy. We targeted the HCN, HCO$^{+}$, HNC, CS and HC$_{3}$N lines, but here we focus on the HCN and HCO$^{+}$ emission. The map covers a field of 1.2' with a ~5" resolution. The HCN and HCO$^{+}$ observations are combined with single dish images. The molecular gas in M82 had been previously found to be distributed in a molecular disk, coincident with the central starburst, and a galactic scale outflow which originates in the central starburst. With the new short spacings-corrected maps we derive some of the properties of the dense molecular gas in the base of the outflow. From the HCN and HCO$^{+}$ J=(1-0) line emission, and under the assumptions of the gas being optically thin and in local thermodynamic equilibrium, we place lower limits to the amount of dense molecular gas in the base of the outflow. The lower limits are $7\times10^{6}$ $M_{\odot}$ and $21\times10^{6}$ $M_{\odot}$, or $\gtrsim2\%$ of the total molecular mass in the outflow. The kinematics and spatial distribution of the dense gas outside the central starburst suggests that it is being expelled through chimneys. Assuming a constant outflow velocity, the derived outflow rate of dense molecular gas is $\geq0.3$ $M_{\odot}$ yr$^{-1}$, which would lower the starburst lifetime by $\geq5\%$. The energy required to expel this mass of dense gas is $(1-10)\times10^{52}$ erg., Comment: 10 pages, 6 figures, 5 tables. Accepted for publication in the ApJ

Using the Sloan Digital Sky Survey (SDSS) data release 4 (DR 4), we investigate the spatial distribution of low and high surface brightness galaxies (LSBGs and HSBGs, respectively). In particular, we focus our attention on the influence of interactions between galaxies on the star formation strength in the redshift range $0.01 < z < 0.1$. With cylinder counts and projected distance to the first and fifth-nearest neighbor as environment tracers, we find that LSBGs tend to have a lack of companions compared to HSBGs at small scales ($<2$ Mpc). Regarding the interactions, we have evidence that the fraction of LSBGs with strong star formation activity increases when the distance between pairs of galaxies ($r_{p}$) is smaller than about four times the Petrosian radius ($r_{90}$) of one of the components. Our results suggest that, rather than being a condition for their formation, the isolation of LSBGs is more connected with their survival and evolution. The effect of the interaction on the star formation strength, measured by the average value of the birthrate parameter $b$, seems to be stronger for HSBGs than for LSBGs. The analysis of our population of LSBGs and HSBGs hosting an AGN show that, regardless of the mass range, the fraction of LSBGs having an AGN is lower than the corresponding fraction of HSBGs with an AGN. Also, we observe that the fraction of HSBGs and LSBGs having an AGN increases with the bulge luminosity. These results, and those concerning the star-forming properties of LSBGs as a function of the environment, fit with the scenario proposed by some authors where, below a given threshold of surface mass density, low surface brightness disks are unable to propagate instabilities, preventing the formation and evolution of massive black holes in the centers of LSBGs., Comment: 33 pages, 13 Figures, 2 Tables. Accepted for publication in The Astrophysical Journal (January 2011 Issue)

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy., Comment: 596 pages. Also available at full resolution at http://www.lsst.org/lsst/scibook

We have developed a web tool to perform Principal Component Analysis (PCA, Murtagh & Heck 1987; Kendall 1980) onto spectral data. The method is especially designed to perform spectral classification of galaxies from a sample of input spectra, giving the set of orthonormal vectors called Principal Components (PCs) and the corresponding projections. The first two projections of the galaxy spectra onto the PCs are known to correlate with the morphological type (Connolly et al. 1995) and, following Galaz & de Lapparent (1998), we use the parameters \delta and \theta which define a spectral classification sequence of typical galaxies from ellipticals to late spirals and star-forming galaxies. The program runs in the website http://azul.astro.puc.cl/PCA/ and can be used without downloading any binary files or building archives of any kind., Comment: 2 pages, 0 figures

Using the APEX sub-millimeter telescope we have investigated the 12CO(3-2) emission in five face-on nearby barred spiral galaxies, where three of them are high surface brightness galaxies (HSBs) lying at the Freeman limit, and two are low surface brightness galaxies (LSBs). We have positive detections for two of three HSB spirals and non-detections for the LSBs. For the galaxies with positive detection (NGC0521 and PGC070519), the emission is confined to their bulges, with velocity dispersions of ~90 and ~73 km/s and integrated intensities of 1.20 and 0.76 K/km/s, respectively. For the non-detections, the estimated upper limit for the integrated intensity is ~0.54 K/km/s. With these figures we estimate the H2 masses as well as the atomic-to-molecular mass ratios. Although all the galaxies are barred, we observe 12CO(3-2) emission only for galaxies with prominent bars. We speculate that bars could dynamically favor the 12CO(3-2) emission, as a second parameter after surface brightness. Therefore, secular evolution could play a major role in boosting collisional transitions of molecular gas, such as 12CO(3-2), especially in LSBs., Comment: 11 pages, 1 figure, ApJ Letters, in press (vol 677)

It is an observational fact that bulges of spiral galaxies contain a high fraction of old and metal-rich stars. Following this observational fact, we have investigated colors of 21 bulges hosted by a selected sample of high surface brightness spirals and low surface brightness galaxies observed in B and R optical bands and in J and Ks near-IR bands. Using structural parameters derived from these observations we obtain evidence that bulges could be formed by pure disk evolution (secular evolution), in agreement with the suggestion by some authors. The color profiles, especially the near-IR ones show null or almost null color gradients, supporting the hypothesis that the disk stellar populations are similar to those present in the bulge, and/or some bulges can be understood as disks with enhanced stellar density (or pseudobulges). In the optical, half of the galaxies present an inverse color gradient, giving additional evidence in favor of secular evolution for the sample investigated. The comparison of the observed colors with those obtained from spectrophotometric models of galaxy evolution suggests that bulges of the selected sample have solar and subsolar metallicity, and are independent of the current stellar formation rate. Also, we obtain evidence suggesting that galaxies hosting small bulges tend to be systematically metal poor compared to those with larger bulges. These results are being checked more carefully with high S/N spectroscopy., Comment: 30 pages, 14 figures. Accepted in the Astronomical Journal. All figures only available at http://www.astro.puc.cl/~ggalaz/figures.html

We present u'g'r'i'BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first ~100 days following discovery. The u'g'BV light curves displayed a double-peaked morphology, which is among Type Ib/Ic supernovae. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u'g'BV was accompanied by the presence in the spectrum of high velocity absorption lines of Fe II, Ca II, and H I. The photospheric velocity derived from spectra at early epochs was unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations which attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 x 10^{51} erg), asymmetric explosion of a massive (8.3 M_sun) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of 1) a polar explosion containing a small fraction of the total mass and moving at high velocity, and 2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast-moving component becomes optically-thin, revealing the slower-moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and gamma ray bursts., Comment: Accepted ApJ on 15 December 2005, 37 pages, 11 figures; minor changes after refereeing process

We investigate the physical nature of blue cores in early-type galaxies through the first multi-wavelength analysis of a serendipitously discovered field blue-nucleated spheroid in the background of the deep ACS/WFC griz multicolor observations of the cluster Abell 1689. The resolved g-r, r-i and i-z color maps reveal a prominent blue core identifying this galaxy as a ``typical'' case study, exhibiting variations of 0.5-1.0 mag in color between the center and the outer regions, opposite to the expectations of reddened metallicity induced gradients in passively evolved ellipticals. From a Magellan-Clay spectrum we secure the galaxy redshift at $z=0.624$. We find a strong X-ray source coincident with the spheroid galaxy. Spectral features and a high X-ray luminosity indicate the presence of an AGN in the galaxy. However, a comparison of the X-ray luminosity to a sample derived from the Chandra Deep Field South displays Lx to be comparable to Type I/QSO galaxies while the optical flux is consistent with a normal star-forming galaxy. We conclude that the galaxy's non-thermal component dominates at high-energy wavelengths while we associate the spheroid blue light with the stellar spectrum of normal star-forming galaxies. We argue about a probable association between the presence of blue cores in spheroids and AGN activity., Comment: Accepted for publication in the Astrophysical Journal. 6 pages, 3 figures. Full resolution images available at http://acs.pha.jhu.edu/~felipe/e-prints

[ABRIDGED] Using the Gaussian+Schechter composite luminosity functions measured from the ESO-Sculptor Survey (de Lapparent et al. 2003), we obtain evidence for evolution in the late spectral class containing late-type Spiral (Sc+Sd) and dwarf Irregular (dI) galaxies. This evolution is detected as an increase of the Sc+Sd+dI galaxy density which can be modeled as either n(z)~1+3(z-0.15) or n(z) ~ (1+z)^2 using the currently favored cosmological parameters Omega_m=0.3 and Omega_Lambda=0.7, with an uncertainty in both evolution rates of order of unity. For Omega_m=1.0 and Omega_Lambda=0.0, the linear and power-law evolution rates are 4 and 2.5 resp. Both models yield a good match to the ESS BVRc redshift distributions to 21-22 mag and to the number-counts to 23-23.5 mag, which probe the galaxy distribution to redshifts z~0.5 and z~1.0 resp. This analysis illustrates how Gaussian+Schechter composite luminosity functions provide more robust constraints on the evolution rate than pure Schechter functions. The detected density evolution indicates that mergers could play a significant role in the evolution of late-type Spiral and dwarf Irregular galaxies. However, the ESO-Sculptor density increase with redshift could also be caused by a ~1 mag brightening of the Sc+Sd+dI galaxies at z~0.5 and a ~1.5-2.0 mag brightening at z~1, which is compatible with the expected passive brightening of Sc galaxies at these redshifts. Distinguishing between luminosity and density evolution is a major difficulty as these produce the same effect on the redshift and magnitude distributions. The detected evolution rate of the ESO-Sculptor Sc+Sd+dI galaxies is nevertheless among the range of measured values from the other existing analyses, whether they provide evidence for density or luminosity evolution., Comment: Accepted for publication in A&A - 25 Pages, 16 color figures, A&A Latex macro

[ABRIDGED] We present the first statistical analysis of the complete ESO-Sculptor redshift survey (ESS). The flux-calibrated sample of 617 galaxy spectra with R_c<20.5 is separated into 3 spectral classes (early, intermediate, and late). We report in detail on the spectral classification, the polynomial K-corrections, and all sources of corresponding random and systematic errors. The derived luminosity functions (LF) in the Johnson-Cousins B and Rc bands are in agreement with the results from the comparable CNOC2 survey (Lin et al. 1999), whereas the ESS provides the first estimates of LFs per spectral type in the Johnson V band. A renewed interpretation of the galaxy LFs from a redshift survey are obtained by fitting the ESS LFs with composite functions based on the local LFs per morphological type (Sandage, Binggeli & Tammann 1985; Jerjen & Tammann 1997). As good or better fits than with pure Schechter functions are obtained using: for the early-type LF, a two-wing Gaussian; for the intermediate-type LF, the sum of a Gaussian modeling the Spiral galaxies and a steep Schechter function (alpha=-1.5) representing the dwarf elliptical galaxies; for the late-type LF, a similar composite function with a flat or weaker slope (-0.80.1 which separates the giant and dwarf galaxy populations., Comment: 33 Pages, 13 color figures, A&A Latex macro. Published in A&A

(Abridged) We present results for J and Ks near-IR imaging data on a large sample of 88 galaxies drawn from the catalogue of Impey et al. (1996). The near-IR data unveils many features of LSBGs not seen before in the optical. First, a high fraction of the observed LSBGs are very luminous in the near-IR, indicating that they have a well developed old stellar population, and that older LSBGs are more frequent in the universe than data from optical bands suggested. Second, the near-IR morphologies are often quite different than seen in the optical. Third, we find significant trends between the near-IR morphologies of the galaxies and their ratio of HI mass to near-IR luminosity. Fourth, we find no trend in disk surface brightness with absolute magnitude, but significant correlations when the bulge surface brightness is used. Finally, we find that the formation of a bulge requires a galaxy to have a total baryonic mass above ~ 10**10 Msun. A wide variety of other correlations are explored for the sample. The strongest of our correlations are with the ratio of HI mass to total baryonic mass, MHI/Mbaryonic, which tracks the evolutionary state of the galaxies as they convert gas into stars, and which ranges from 0.05 up to nearly 1 for the galaxies in our sample. We see also trends between MHI/Mbaryonic and central surface density, suggesting that increased star formation efficiency with increasing gas surface density strongly drives the conversion of gas into stars., Comment: Accepted in the Astronomical Journal. 48 pages, 20 Figures

Recently acquired near-IR imaging (J and Ks) of low surface brightness galaxies is presented. The data includes 52 galaxies with log[MHI/Msolar] < 9.0 and 58 galaxies with log[MHI/Msolar] > 9.5. These galaxies have been selected from the catalogue of Impey et al. (1996), and all of them are observable from both hemispheres. The principal goal of this research is to investigate the poorly understood giant and old stellar content of these galaxies. Current work includes total and isophotal photometry, and comparison with spectrophotometric models of galaxy evolution, including the role of age and metallicity. Already allocated observing time at Las Campanas Observatory will provide high S/N B and I imaging., Comment: To appear in ``Stars, Gas, and Dust in Galaxies: Exploring the Links'', CTIO/ESO/LCO Workshop, La Serena, Chile, March 2000; Eds. D. Alloin, K. Olsen, & G. Galaz, ASP Conf. Ser., 4 pages text, 2 figures. Uses newpasp.sty

(Abridged) We present near-IR photometry of a selected sample of southern hemisphere E+A galaxies. The sample includes 50 galaxies from nearby and distant clusters as well as E+A galaxies from the field. The photometry includes J, H and Ks apparent magnitudes and colors. Observed colors are obtained from the apparent total magnitudes and compared to spectrophotometric models of galaxy evolution GISSEL96. There is an overall agreement between integrated colors of models and observed ones, for both the E+A located in clusters and in the field, at z~0.1. However, large differences are found between colors predicted from models and those observed in E+A galaxies located in more distant clusters. We investigate systematic properties of the E+A sample as a function of their environment. Results seem to indicate that cluster E+As (at low redshift) are bluer than field E+As at z~0.1. Even this conclusion does not depend whether we use comoving or rest-frame colors, nor on the models used to obtain rest-frame colors; the difference is not significant enough, considering color dispersions between the samples. If differences are real, they could imply different stellar content for the E+A galaxies located in the field, compared to the cluster E+A., Comment: Accepted for publication in the Astronomical Journal. 48 pages, uses AAS LaTeX macros v5.0. Includes 2 tables, 9 figures

I present near-IR photometry of a selected sample of E+A galaxies observed in the southern hemisphere. The sample includes 50 galaxies from nearby clusters (z ~ 0.05) and distant clusters (z ~ 0.31) as well as E+A galaxies from the field (z ~ 0.15). I have also observed 13 normal early-type galaxies from the field and from clusters, to be compared with the E+A sample. The photometry includes J, H and Ks apparent magnitudes and colors. I investigate systematic properties of the E+A sample as a function of their environment, contrasting the observed colors with spectrophotometric models of galaxy evolution., Comment: To appear in proceedings of conference on Clustering At High Redshift, ASP Conf. Series, ed. A. Mazure and O.Le Fevre (Marseilles, July 1999). 2 pages, 1 postscript figure, newpasp.sty

We briefly show results on the redshift and space distribution of field galaxies with different spectral types in the ESO-Sculptor survey (ESS). We also show results on the ESS galaxy luminosity function., Comment: 4 pages, 2 Postscript figures. To appear in `Wide-field Surveys in Cosmology', proceedings of XIV IAP meeting. Uses conf_iap.sty

Using the ESO-Sculptor galaxy redshift survey data (ESS), we have extensively tested the Principal Components Analysis (PCA) method to perform the spectral classification of galaxies with $z \la$ 0.5. This method allows us to classify all galaxies in an ordered and continuous spectral sequence, which is strongly correlated with the morphological type. The PCA allows to quantify the systematic physical properties of the galaxies in the sample, like the different stellar contributions to the observed light as well as the stellar formation history. We also examine the influence of the emission lines, and the signal-to-noise ratio of the data. This analysis shows that the emission lines play a significant role in the spectral classification, by tracing the activity and abnormal spectral features of the observed sample. The PCA also provides a powerful tool to filter the noise which is carried by the ESS spectra. By comparison of the ESS PCA spectral sequence with that for a selected sample of Kennicutt galaxies (Kennicutt 1992a), we find that the ESS sample contains 26% of E/S0, 71% of Sabc and 3% of Sm/Irr. The type fractions for the ESS show no significant changes in the redshift interval $z \sim 0.1-0.5$, and are comparable to those found in other galaxy surveys at intermediate redshift. The PCA can be used independently from any set of synthetic templates, providing a completely objective and unsupervised method to classify spectra. We compare the classification of the ESS sample given by the PCA, with a $\chi^2$ test between the ESS sample and galaxy templates from Kennicutt (Kennicutt 1992a), and obtain results in good agreement. The PCA results are also in agreement with the visual morphological classification carried out for the 35 brightest galaxies in the survey., Comment: LaTeX, 18 Postscript figures, 23 pages. Accepted for publication in Astro. & Astroph. Suppl