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We present a detailed imaging analysis of 260 ks of sub-arcsecond resolution Chandra Advanced CCD Imaging Spectrometer (ACIS-S) observations of the nearby Seyfert 2 galaxy NGC 5728. Our study focuses on the bright and diffuse soft X-ray emission within the galaxy's inner ~1 kpc. By comparing the X-ray emission across different energy bands, we identify localized variations in the absorbing column and emission processes. We observe more X-ray absorption in the direction perpendicular to the bicone, which is co-located with an inner warped CO disk in the galaxy. The innermost region, which shows the strongest excess of hard X-ray emission, is spatially coincident with the CO(2-1) emission from ALMA and dusty spirals observed in a Hubble Space Telescope V-H color map. We detect soft extended emission associated with the circumnuclear star-forming ring at ~1 kpc, suggestive of hot gas with kT=0.44 keV. We derive measurements for the hot gas mass, M=7.9x10^5 solar masses, pressure, p=2.0x10^-10 dyne per square cm, and cooling times, t=193.2 Myr. In the vicinity of the star-forming ring, we detect two X-ray point sources with soft X-ray spectra and 0.3-7 keV luminosities L~8x10^38 erg per second. These properties suggest X-ray binaries., Comment: Accepted for publication on ApJ

Exploring SMBH population in protoclusters offers valuable insights into how environment affects SMBH growth. However, research on AGN within these areas is still limited by the small number of protoclusters known at high redshift and by the availability of associated deep X-ray observations. To understand how different environments affect AGN triggering and growth at high redshift, we investigated the X-ray AGN population in the field of the MUSE Quasar Nebula 01 (MQN01) protocluster at z ~3.25. This field is known for hosting the largest Lya nebula in the Borisova+16 sample, and one of the largest overdensities of UV-continuum selected and sub-mm galaxies found so far at this redshift. We conducted a ultra deep Chandra X-ray survey (634 ks) observation of the MQN01 field and produced a comparative analyses of the properties of the X-ray AGNs detected in MQN01 against those observed in other selected protoclusters, such as Spiderweb and SSA22. By combining the X-ray, deep MUSE and ALMA data of the same field, we identified six X-ray AGNs within a volume of 16 cMpc^2 and \pm 1000 km/s, corresponding to an X-ray AGN overdensity of ~1000. This overdensity increases at the bright end, exceeding what was observed in the Spiderweb and SSA22 within similar volumes. The AGN fraction measured in MQN01 is significantly higher (f_AGN > 20%) than in the field and increases with stellar masses, reaching a value of 100% for log(M*/Msun) > 10.5. Lastly, we observe that the average specific accretion rate (\lambda_sBHAR) for SMBH populations in MQN01 is higher than in the field and other protoclusters, generally increasing as one moves toward the center of the overdensity. Our results, especially the large fraction of highly accreting SMBHs in the inner regions of the MQN01 overdensity, suggest that protocluster environments offer ideal physical conditions for SMBH triggering and growth., Comment: 19 pages, 13 figures, submitted on the A&A on September 9, 2024

We present a multi-wavelength analysis of MCG+11-11-032, a nearby AGN with the unique classification of both a binary and a dual AGN candidate. With new Chandra observations we aim to resolve any dual AGN system via imaging data, and search for signs of a binary AGN via analysis of the X-ray spectrum. Analyzing the Chandra spectrum, we find no evidence of previously suggested double-peaked Fe K$\alpha$ lines; the spectrum is instead best fit by an absorbed powerlaw with a single Fe K$\alpha$ line, as well as an additional line centered at $\approx$7.5 keV. The Chandra observation reveals faint, soft, and extended X-ray emission, possibly linked to low-level nuclear outflows. Further analysis shows evidence for a compact, hard source -- MCG+11-11-032 X2 -- located 3.27'' from the primary AGN. Modeling MCG+11-11-032 X2 as a compact source, we find that it is relatively luminous ($L_{\text{2$-$10 keV}} = 1.52_{-0.48}^{+0.96}\times 10^{41}$ erg s$^{-1}$), and the location is coincident with an compact and off-nuclear source resolved in Hubble Space Telescope infrared (F105W) and ultraviolet (F621M, F547M) bands. Pairing our X-ray results with a 144 MHz radio detection at the host galaxy location, we observe X-ray and radio properties similar to those of ESO 243-49 HLX-1, suggesting that MCG+11-11-032 X2 may be a hyper-luminous X-ray source. This detection with Chandra highlights the importance of a high-resolution X-ray imager, and how previous binary AGN candidates detected with large-aperture instruments benefit from high-resolution follow-up. Future spatially resolved optical spectra, and deeper X-ray observations, can better constrain the origin of MCG+11-11-032 X2., Comment: 16 pages, 7 figures, submitted to ApJ

The Chandra Source Catalog (CSC) is a virtual X-ray astrophysics facility that enables both detailed individual source studies and statistical studies of large samples of X-ray sources detected in ACIS and HRC-I imaging observations obtained by the Chandra X-ray Observatory. The catalog provides carefully-curated, high-quality, and uniformly calibrated and analyzed tabulated positional, spatial, photometric, spectral, and temporal source properties, as well as science-ready X-ray data products. The latter includes multiple types of source- and field-based FITS format products that can be used as a basis for further research, significantly simplifying followup analysis of scientifically meaningful source samples. We discuss in detail the algorithms used for the CSC Release 2 Series, including CSC 2.0, which includes 317,167 unique X-ray sources on the sky identified in observations released publicly through the end of 2014, and CSC 2.1, which adds Chandra data released through the end of 2021 and expands the catalog to 407,806 sources. Besides adding more recent observations, the CSC Release 2 Series includes multiple algorithmic enhancements that provide significant improvements over earlier releases. The compact source sensitivity limit for most observations is ~5 photons over most of the field of view, which is ~2x fainter than Release 1, achieved by co-adding observations and using an optimized source detection approach. A Bayesian X-ray aperture photometry code produces robust fluxes even in crowded fields and for low count sources. The current release, CSC 2.1, is tied to the Gaia-CRF3 astrometric reference frame for the best sky positions for catalog sources., Comment: 66 pages, 17 figures, 16 tables, accepted for publication in The Astrophysical Journal Supplement Series

We explore the evolution of the ~107 degree hot gas in normal galaxies out to redshift = 0.5 (lookback time = 5 Gyr), using X-ray luminosity functions (XLF) built from a sample of 575 normal galaxies with z < 0.6 detected in five high galactic latitude Chandra wide-field surveys. After estimating the emission due to the hot gas component (reducing the sample to ~400 galaxies), we compared the XLF in three redshift bins (z = 0.1, 0.3, and 0.5), finding increases in the number of galaxies per unit co-moving volume from z = 0.1 to 0.3 and then from z = 0.3 to 0.5. These XLF changes suggest a significant (~5s) X-ray luminosity evolution of the hot gas, with LX,GAS decreasing by a factor of 6-10 in the last 5 Gyr (from z = 0.5 to 0.1). The relative abundance of LX,GAS~1041 erg s-1 galaxies at higher z, suggests that high z, moderate LX,GAS galaxies may be the optimal target to solve the missing baryon problem. In early-type galaxies, this observational trend is qualitatively consistent with (but larger than) the expected time-dependent mass-loss rate in cooling flow models without AGN feedback. In late-type galaxies, the observational trend is also qualitatively consistent with (but larger than) the effect of the z-dependent SFR., Comment: 29 pages, 14 figures, new Appendix added, accepted for publication in ApJ

We report the identification of a quasar overdensity in the BOSSJ0210 field, dubbed Cosmic Himalayas, consisting of 11 quasars at $z=2.16-2.20$, the densest overdensity of quasars ($17\sigma$) in the $\sim$10,000 deg$^2$ of the Sloan Digital Sky Survey. We present the spatial distributions of galaxies and quasars and an HI absorption map of the intergalactic medium (IGM). On the map of 465 galaxies selected from the MAMMOTH-Subaru survey, we find two galaxy density peaks that do not fall on the quasar overdensity but instead exist at the northwest and southeast sides, approximately 25 $h^{-1}$ comoving-Mpc apart from the quasar overdensity. With a spatial resolution of 15 $h^{-1}$ comoving Mpc in projection, we produce a three-dimensional HI tomography map by the IGM Ly$\alpha$ forest in the spectra of 23 SDSS/eBOSS quasars behind the quasar overdensity. Surprisingly, the quasar overdensity coincides with neither an absorption peak nor a transmission peak of IGM HI but lies near the border separating opaque and transparent volumes, with the more luminous quasars located in an environment with lesser IGM HI. Hence remarkably, the overdensity region traced by the 11 quasars, albeit all in coherently active states, has no clear coincidence with peaks of galaxies or HI absorption densities. Current physical scenarios with mixtures of HI overdensities and quasar photoionization cannot fully interpret the emergence of Cosmic Himalayas, suggesting this peculiar structure is an excellent laboratory to unveil the interplay between galaxies, quasars, and the IGM., Comment: 19 pages, 11 figures, submitted to ApJ, comments are welcome

We present the analysis of the rest frame ultraviolet and optical spectra of 30 bright blue quasars at $z\sim3$, selected to examine the suitability of AGN as cosmological probes. In our previous works, we found an unexpectedly high fraction ($\approx 25 \%$) of X-ray weak quasars in the sample. The latter sources also display a flatter UV continuum and a broader and fainter CIV profile in the archival UV data with respect to their X-ray normal counterparts. Here we present new observations with the LBT in both the $zJ$ (rest-frame $\simeq$2300-3100 $\rm \mathring{A}$) and the $K_S$ ($\simeq$4750-5350 $\rm \mathring{A}$) bands. We estimated black hole masses ($M_{\rm BH}$) and Eddington ratios ($\lambda_{\rm Edd}$) from the from the H$\beta$ and MgII emission lines, finding that our $z\sim3$ quasars are on average highly accreting ($\langle \lambda_{\rm Edd} \rangle\simeq 1.2$ and $\langle M_{\rm BH} \rangle\simeq 10^{9.7}M_\odot$), with no difference in $\lambda_{\rm Edd}$ or $M_{\rm BH}$ between X-ray weak and X-ray normal quasars. From the $zJ$ spectra, we derive flux and equivalent width of MgII and FeII, finding that X-ray weak quasars display higher FeII/MgII ratios with respect to typical quasars. FeII/MgII ratios of X-ray normal quasars are instead consistent with other estimates up to $z\simeq6.5$, corroborating the idea of already chemically mature BLRs at early cosmic time. From the $K_S$ spectra, we find that all the X-ray weak quasars present generally weaker [OIII] emission (EW<10 $\rm \mathring{A}$) than the normal ones. The sample as a whole, however, abides by the known X-ray/[OIII] luminosity correlation, hence the different [OIII] properties are likely due to an intrinsically weaker [OIII] emission in X-ray weak objects, associated to the shape of the spectral energy distribution. We interpret these results in the framework of accretion-disc winds., Comment: 25 pages, 17 figures, Accepted for publication on Astronomy & Astrophysics

X-ray appearance of normal galaxies is mainly determined by X-ray binaries powered by accretion onto a neutron star or a stellar mass black hole. Their populations scale with the star-formation rate and stellar mass of the host galaxy and their X-ray luminosity distributions show a significant split between star-forming and passive galaxies, both facts being consequences of the dichotomy between high- and low-mass X-ray binaries. Metallicity, IMF and stellar age dependencies, and dynamical formation channels add complexity to this picture. The numbers of high-mass X-ray binaries observed in star-forming galaxies indicate quite high probability for a massive star to become an accretion powered X-ray source once upon its lifetime. This explains the unexpectedly high contribution of X-ray binaries to the Cosmic X-ray Background, of the order of $\sim 10\%$, mostly via X-ray emission of faint star-forming galaxies located at moderate redshifts which may account for the unresolved part of the CXB. Cosmological evolution of the $L_X-{\rm SFR}$ relation can make high-mass X-ray binaries a potentially significant factor in (pre)heating of intergalactic medium in the early Universe., Comment: Invited chapter for the Handbook of X-ray and Gamma-ray Astrophysics. Editors: Cosimo Bambi, Andrea Santangelo. Publisher: Springer Singapore, 2023

We present an extensive and well-characterized Chandra X-ray Galaxy Catalog (CGC) of 8557 galaxy candidates in the redshift range z ~ 0.04 - 0.7, optical luminosity 1010 - 1011 Lro, and X-ray luminosity (0.5-7 keV) LX = 2x1040 - 2x1043 erg s-1. We estimate ~5% false match fraction and contamination by QSOs. The CGC was extracted from the Chandra Source Catalog version 2 (CSC2) by cross-correlating with optical and IR all-sky survey data, including SDSS, PanSTARRS, DESI Legacy, and WISE. Our selection makes use of two main criteria that we have tested on the subsample with optical spectroscopical identification. (1) A joint selection based on X-ray luminosity (LX) and X-ray to optical flux ratio (FXO), which recovers 63% of the spectroscopically classified galaxies with a small contamination fraction (7%), a significant improvement over methods using LX or FXO alone (< 50% recovery). (2) A joint W1-W2 (W12) WISE color and LX selection that proves effective in excluding QSOs and improves our selection by recovering 72% of the spectroscopically classified galaxies and reducing the contamination fraction (4%). Of the CGC, 24% was selected by means of optical spectroscopy; 30% on the basis of LX, FXO, and W12; and 46% by using either the LX-FXO or the LX-W12 selection criteria. We have individually examined the data for galaxies with z < 0.1, which may include more than one CSC2 X-ray source, leading to the exclusion of 110 local galaxies. Our catalog also includes near-IR and UV data and galaxy morphological types., Comment: Accepted in ApJS, 37 pages, 11 figures; Minor revisions

X-ray bright optically normal galaxies (XBONGs) are galaxies with X-ray luminosities consistent with those of active galactic nuclei (AGNs) but no evidence of AGN optical emission lines. Crossmatching the Chandra Source Catalog version 2 (CSC2) with the Sloan Digital Sky Survey (SDSS) sample of spectroscopically classified galaxies, we have identified 817 XBONG candidates with LX > 1042 erg s-1 and X-ray to optical flux ratio FXO > 0.1. Comparisons with WISE colors and NIR, optical, UV, and radio luminosities show that the loci of XBONGs are in-between those of control samples of normal galaxies and quasars and are consistent with low-luminosity quasars. We find that 43% of the XBONG sample have X-ray colors suggesting NH > 1022 cm-2, double the fraction in the QSO sample, suggesting that a large fraction of XBONG are highly obscured AGNs. However, ~50% of the XBONGs are not obscured and have X-ray colors harder than those of normal galaxies. Some of these XBONGs have spatially extended X-ray emission. These characteristics suggest that they may be unidentified galaxy groups and clusters. Using the X-ray luminosity functions of QSOs and galaxies/groups/clusters, we estimate the approximate fraction of extended XBONGs to be < 20%. We also assess the approximate fraction of XBONGs whose AGN signatures are diluted by stellar light of host galaxies to be ~30%, based on their redshift and deviation from the extrapolation of the QSO LX-Lr relation., Comment: Accepted in ApJ. 33 pages, 17 figures; minor revisions

Recent deep Chandra observations of nearby Compton thick (CT) AGN have produced surprising results, uncovering extended emission not only in the soft X-rays but in the hard emission (>3 keV), challenging the long-held belief that the characteristic hard X-ray continuum and fluorescent Fe Ka lines are associated with the torus in the standard picture of AGN. In this work, we present the analysis of our deep (~261 ks) X-ray Chandra ACIS-S observations of NGC 5728, a nearby (z=0.00932) CT AGN. We find that the diffuse emission is more extended at lower energies, in the bicone direction out to ~2 kpc radially, but also significantly extended in the direction of the cross-cone, out to ~1.4 kpc. Our results suggest that the ratio of detected photons in the cross-cone to the bicone region is ~16%, below 3 keV, decreasing to 5% for energies 3-6 keV. The nuclear spectrum suggests a low photoionization phase mixed with a more ionized gas component, while the bicone and cross-cone spectra are dominated by a mix of photoionization and shocked gas emission. A mixture of thermal and photoionization models to fit the spectra indicates the presence of complex gas interactions, consistent with previous observations of other CT AGN (e.g., ESO 428-G014).

We present Chandra ACIS-S imaging spectroscopy results of the extended (1.5''- 8'', 300 pc-1600 pc) hard X-ray emission of NGC 5728, the host galaxy of a Compton thick active galactic nucleus (CT AGN). We find spectrally and spatially-resolved features in the Fe K$\alpha$ complex (5.0-7.5 keV), redward and blueward of the neutral Fe line at 6.4 keV in the extended narrow line region bicone. A simple phenomenological fit of a power law plus Gaussians gives a significance of 5.4$\sigma$ and 3.7$\sigma$ for the red and blue wings, respectively. Fits to a suite of physically consistent models confirm a significance $\geq$3$\sigma$ for the red wing. The significance of the blue wing may be diminished by the presence of rest frame highly ionized Fe XXV and Fe XXVI lines (1.4$\sigma$ - 3.7$\sigma$ range). A detailed investigation of the Chandra ACIS-S point spread function (PSF) and comparison with the observed morphology demonstrates that these red and blue wings are radially extended (~5'', ~1 kpc) along the optical bicone axis. If the wings emission is due solely to redshifted and blueshifted high-velocity neutral Fe K$\alpha$ then the implied line-of-sight velocities are +/- ~0.1c, and their fluxes are consistent with being equal. A symmetric high-velocity outflow is then a viable explanation. This outflow has deprojected velocities ~100 times larger than the outflows detected in optical spectroscopic studies, potentially dominating the kinetic feedback power., Comment: Accepted for publication on ApJ

Kilo-parsec scale hard ($>$ 3 keV) X-ray continuum and fluorescent Fe K$\alpha$ line emission has been recently discovered in nearby Compton-thick (CT) active galactic nuclei (AGN), which opens new opportunities to improve AGN torus modeling and investigate how the central supermassive black hole interacts with and impacts the host galaxy. Following a pilot Chandra survey of nearby CT AGN, we present in this paper the Chandra spatial analysis results of five uniformly selected non-CT but still heavily obscured AGN to investigate the extended hard X-ray emission by measuring the excess emission counts, excess fractions, and physical scales. Three of them show extended emission in the 3.0-7.0 keV band detected at $>$ 3$\sigma$ above the Chandra PSF with total excess fractions ranging from $\sim$8% - 20%. The extent of the hard emission ranges from at least $\sim$250 pc to 1.1 kpc in radius. We compare these new sources with CT AGN and find that CT AGN appear to be more extended in the hard band than the non-CT AGN. Similar to CT AGN, the amounts of extended hard X-ray emission relative to the total emission of these obscured AGN are not negligible. Together with other extended hard X-ray detected AGN in the literature, we further explore potential correlations between the extended hard X-ray component and AGN parameters. We also discuss the implications for torus modeling and AGN feedback. Considering potential contributions from X-ray binaries (XRBs) to the extended emission, we do not see strong XRB contamination in the overall sample., Comment: 14 pages, 12 figures; Accepted for publication in ApJ. arXiv admin note: text overlap with arXiv:2008.02175

We present $Chandra$ ACIS imaging spectroscopy of the nucleus of the Seyfert 2 Galaxy Mrk 34. We identify spatially and spectrally resolved features in the band that includes Fe K$\alpha$, Fe XXV and Fe XXVI. These features indicate high-velocity ($\gtrsim15,000\,\rm{km\,s}^{-1}$ line-of-sight) material separated spanning $\sim$0.5 arcsec, within $\sim200$ pc of the nucleus. This outflow could have deprojected velocities $\sim12-28\times$ greater than the [O III] emitting outflows, and could potentially dominate the kinetic power in the outflow. This emission may point to the origins of the optical and X-ray winds observed at larger radii, and could indicate a link between ultra-fast outflows and AGN feedback on $\gtrsim$kpc scales., Comment: 13 pages, 7 figures. Resubmitted to ApJ with revisions

We report the results of joint Chandra/ACIS - NuSTAR deep observations of NGC 1167, the host galaxy of the young radio jet B2 0258+35. In the ACIS data we detect X-ray emission, extended both along and orthogonal to the jet. At the end of the SE radio jet, we find lower-energy X-ray emission that coincides with a region of CO turbulence and fast outflow motions. This suggests that the hot Interstellar Medium (ISM) may be compressed by the jet and molecular outflow, resulting in more efficient cooling. Hydrodynamic simulations of jet-ISM interaction tailored to NGC 1167 are in agreement with this conclusion and with the overall morphology and spectra of the X-ray emission. The faint hard nuclear source detected with Chandra and the stringent NuSTAR upper limits on the harder X-ray emission show that the active galactic nucleus (AGN) in NGC 1167 is in a very low-accretion state. However, the characteristics of the extended X-ray emission are more consonant to those of luminous Compton Thick AGNs, suggesting that we may be observing the remnants of a past high accretion rate episode, with sustained strong activity lasting ~ 2 x 103 yr. We conclude that NGC1167 is presently a LINER, but was an AGN in the past, given the properties of the extended X-ray emission and their similarity with those of CT AGN extended emission., Comment: ApJ, in press

The non-linear relation between the X-ray and ultraviolet (UV) luminosity in quasars has been used to derive quasar distances and to build a Hubble diagram at redshifts up to $z\sim$ 7. This cosmological application is based on the assumption of independence of the relation on redshift and luminosity. We want to test the reliability of this hypothesis by studying the spectroscopic properties of high-redshift quasars in the X-ray and UV bands. We performed a one-by-one analysis of a sample of 130 quasars at $z>$ 2.5 with high-quality X-ray and UV spectroscopic observations. We found that not only the X-ray to UV correlation still holds at these redshifts, but its intrinsic dispersion is as low as 0.12 dex (previous works reached 0.20$-$0.22 dex). For a sample of quasars at $z\sim$ 3 with particularly high-quality observations the dispersion further drops to 0.09 dex, a value entirely accountable for by intrinsic variability and source geometry effects. The composite spectra of these quasars, in both the X-rays and the UV, do not show any difference with respect to the average spectra of quasars at lower redshifts. The absence of any spectral difference between high- and low-$z$ quasars and the tightness of the X-ray to UV relation suggests that no evolutionary effects are present in the relation. Therefore, it can be safely employed to derive quasar distances. Under this assumption, we obtain a measurement of the luminosity distance at $z\sim$ 3 with 15 % uncertainty, and in a 4$\sigma$ tension with the concordance model., Comment: Accepted for publication in Astronomy & Astrophysics Letters, 8 pages, 6 figures

Sub-arcsecond imaging of the X-ray emission in the type 2 AGN Mrk 78 with Chandra shows complex structure with spectral variations on scales from $\sim$200 pc to $\sim$ 2 kpc. Overall the X-ray emission is aligned E-W with the radio (3.6 cm) and narrow emission line region as mapped in [OIII], with a marked E-W asymmetry. The Eastern X-ray emission is mostly in a compact knot coincident with the location where the radio source is deflected, while the Western X-ray emission forms a loop or shell $\sim$2 kpc from the nucleus with radius $\sim$0.7 kpc. There is suggestive evidence of shocks in both the Eastern knot and the Western arc. Both these positions coincide with large changes in the velocities of the [OIII] outflow. We discuss possible reasons why the X-ray shocks on the Western side occur $\sim1$ kpc farther out than on the Eastern side. We estimate that the thermal energy injected by the shocks into the interstellar medium corresponds to $0.05-0.6$% of the AGN bolometric luminosity., Comment: 23 pages, 14 figures, 6 tables

Imaging X-ray spectroscopy of nearby AGNs, mostly with Chandra, has shown that extended soft (<2.5 keV) emission-line dominated X-ray biconical structures, of kiloparsec scale, are widespread in highly absorbed Compton Thick (CT) AGNs. The X-ray emission is complex, requiring both photoionized and shock-ionized gas. It originates from high ionization regions and is surrounded by cocoons of low ionization narrow line emission regions (LINERS). Bicone 3-6 keV continuum and 6.4 keV Fe Kalpha emission has been detected, contrary to the standard AGN model expectation that would confine this hard emission to the pc-size nuclear absorbing torus. Extended emission in the cross-cone direction, also requires modifications to the AGN standard model. A porous torus, with a significant fraction of escaping AGN continuum, and/or jet interaction with ISM creating a blow-back towards the nuclear region seem to be required. Here we discuss these results and their implications for both the AGN model and our understanding of AGN feedback. The finding of hot and highly photoionized gas on 10s parsecs to several kiloparsec scales demonstrates that all three feedback mechanisms are at work: radiation affects the inner molecular clouds of the host on a ~1 kpc scale; shocks of relativistic jets with the host ISM a few kpc from the central AGN; and photoionization of the ISM via winds on scales from pc to multiple kpc. These results demonstrate that X-rays are needed to develop a complete picture of AGN/host interaction along with radio continuum, mm and sub-mm molecular line emission, and optical/near-IR emission lines., Comment: This is a review mostly based on Chandra results on the extended X-ray emission of AGNs. It will be included in the Section on Galaxies of the Handbook on X-ray and Gamma ray Astrophysics, A. Santangelo and C. Bambi (eds.), Springer. Comments welcome

We present a detailed spectral and imaging analysis of the central $15''$ radius ($\sim 7.5 \text{ kpc}$) region of the merger galaxy NGC 6240 that makes use of all the available \textit{Chandra}-ACIS data ($0.3 - 3 \text{ keV}$ effective exposure of $\sim 190 \text{ ks}$). This region shows extended X-ray structures with lower energy counterparts imaged in CO, [O III] and H$\alpha$ line emission. We find both photo-ionized phases of possible nuclear excitation and thermal shock-excited emission in the different large-scale components: the north-west "loop" detected in H$\alpha$, the region surrounding the two nuclei, the large outflow region to the north-east detected in [O III], and the southern X-ray extensions. The latter could be the ionization cone of the northern nucleus, with the N counterpart being obscured by the galaxy disk. The radial distribution of the X-ray surface brightness suggests a confined hot interstellar medium at $r < 2.5 \text{ kpc}$, with a free-flowing wind at larger radii; if the confinement is magnetic, we estimate B-field values of $\sim 100\,\mu \text{G}$ , similar to those measured in the halo of M82. The thermal gas of the extended halo at $kT \sim 1 \text{ keV}$ absorbs soft X-rays from the AGN, but not the extreme ultraviolet radiation leading to a rapid increase in $F_{\text{[O III]}}/F_{\text{X}}$ beyond $\sim 3 \text{ kpc}$. The $\alpha$ element to Fe abundance ratios of the thermal components in the different regions of the extended X-ray emission are generally compatible with SNe II yields, confirming the importance of the active star formation in NGC 6240., Comment: 36 pages, 16 figures, 4 tables, accepted for publication on ApJ

We report the discovery of statistically significant spatial structures in the projected two-dimensional distributions of the Globular Cluster (GC) systems of 10 among the brightest galaxies in the Fornax Cluster. We use a catalog of GCs extracted from the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Fornax Cluster Survey (ACSFCS) imaging data. We characterize the size, shape and location relative to the host galaxies of the GC structures and suggest a classification based on their morphology and location that is suggestive of different formation mechanisms. We also investigate the GC structures in the context of the positions of their host galaxies relative to the general spatial distributions of galaxies and intra-cluster globular clusters in the Fornax Cluster. We finally estimate the dynamical masses of the progenitors of some GC structures, under the assumption that they are the relics of past accretion events of satellite galaxies by their hosts., Comment: 40 pages, 26 figures, accepted for publication in ApJ

We present a study of the relation between X-rays and ultraviolet emission in quasars for a sample of broad-line, radio-quiet objects obtained from the cross-match of the Sloan Digital Sky Survey DR14 with the latest Chandra Source Catalog 2.0 (2,332 quasars) and the Chandra COSMOS Legacy survey (273 quasars). The non-linear relation between the ultraviolet (at 2500 A, $L_{O}$) and the X-ray (at 2 keV, $L_{X}$) emission in quasars has been proved to be characterised by a smaller intrinsic dispersion than the observed one, as long as a homogeneous selection, aimed at preventing the inclusion of contaminants in the sample, is fulfilled. By leveraging on the low background of Chandra, we performed a complete spectral analysis of all the data available for the SDSS-CSC2.0 quasar sample (i.e. 3,430 X-ray observations), with the main goal of reducing the uncertainties on the source properties (e.g. flux, spectral slope). We analysed whether any evolution of the $L_{X}-L_{O}$ relation exists by dividing the sample in narrow redshift intervals across the redshift range spanned by our sample, $z \simeq 0.5-4$. We find that the slope of the relation does not evolve with redshift and it is consistent with the literature value of $0.6$ over the explored redshift range, implying that the mechanism underlying the coupling of the accretion disc and hot corona is the same at the different cosmic epochs. We also find that the dispersion decreases when examining the highest redshifts, where only pointed observations are available. These results further confirm that quasars are `standardisable candles', that is we can reliably measure cosmological distances at high redshifts where very few cosmological probes are available., Comment: 20 pages, 14 figures, accepted for publication in A&A

In this paper, we present an approach to evaluate Research \& Development (R\&D) performance based on the Analytic Hierarchy Process (AHP) method. Through a set of questionnaires submitted to a team of experts, we single out a set of indicators needed for R\&D performance evaluation. The indicators, together with the corresponding criteria, form the basic hierarchical structure of the AHP method. The numerical values associated with all the indicators are then used to assign a score to a given R\&D project. In order to aggregate consistently the values taken on by the different indicators, we operate on them so that they are mapped to dimensionless quantities lying in a unit interval. This is achieved by employing the empirical Cumulative Density Function (CDF) for each of the indicators. We give a thorough discussion on how to assign a score to an R\&D project along with the corresponding uncertainty due to possible inconsistencies of the decision process. A particular example of R\&D performance is finally considered., Comment: 13 pages, 2 figures

We report the analysis of the deep (270 ks) X-ray Chandra data of one of the most radio-loud, Seyfert 2 galaxies in the nearby Universe (z=0.01135), IC 5063. The alignment of the radio structure with the galactic disk and ionized bi-cone, enables us to study the effects of both radio jet and nuclear irradiation on the interstellar medium (ISM). The nuclear and bi-cone spectra suggest a low photoionization phase mixed with a more ionized or thermal gas component, while the cross-cone spectrum is dominated by shocked and collisionally ionized gas emission. The clumpy morphology of the soft (<3 keV) X-ray emission along the jet trails, and the large (~2.4 kpc) filamentary structure perpendicular to the radio jets at softer energies (<1.5 keV), suggest a large contribution of the jet-ISM interaction to the circumnuclear gas emission. The hard X-ray continuum (>3 keV) and the Fe K-alpha 6.4 keV emission are both extended to kpc size along the bi-cone direction, suggesting an interaction of nuclear photons with dense clouds in the galaxy disk, as observed in other Compton Thick (CT) active nuclei. The north-west cone spectrum also exhibits an Fe XXV emission line, which appears spatially extended and spatially correlated with the most intense radio hot-spot, suggesting jet-ISM interaction., Comment: 28 pages, 10 figures and 3 tables (with 10 more figures and 3 more tables in the Appendix), submitted to ApJ on May 24, 2021

We analyse the properties of the CIV broad emission line in connection with the X-ray emission of 30 bright SDSS quasars at z~3.0-3.3 with pointed XMM-Newton observations, which were selected to test the suitability of AGN as cosmological tools. In our previous work, we found that a large fraction (~25%) of the quasars in this sample are X-ray underluminous by factors of >3-10. As absorbing columns of >10$^{23}$ cm$^{-2}$ can be safely ruled out, their weakness is most likely intrinsic. Here we explore possible correlations between the UV and X-ray features of these sources to investigate the origin of X-ray weakness. We fit their UV SDSS spectra and analyse their CIV properties (e.g., equivalent width, EW; line peak velocity, $\upsilon_{\rm peak}$) as a function of the X-ray photon index and 2-10 keV flux. We confirm the trends of CIV $\upsilon_{\rm peak}$ and EW with UV luminosity at 2500 angstrom for both X-ray weak and X-ray normal quasars, as well as the correlation between X-ray weakness and CIV EW. In contrast to some recent work, we do not observe any clear relation between the 2-10 keV luminosity and $\upsilon_{\rm peak}$. We find a correlation between the hard X-ray flux and the integrated CIV flux for X-ray normal quasars, whilst X-ray weak quasars deviate from the main trend by more than 0.5 dex. We argue that X-ray weakness might be interpreted in a starved X-ray corona picture associated with an ongoing disc-wind phase. If the wind is ejected in the vicinity of the black hole, the extreme-UV radiation that reaches the corona will be depleted, depriving the corona of seeds photons and generating an X-ray weak quasar. Yet, at the largest UV luminosities (>10$^{47}$ erg s$^{-1}$), there will still be an ample reservoir of ionising photons that can explain the excess CIV emission observed in the X-ray weak quasars with respect to normal sources of similar X-ray luminosities., Comment: 22 pages, 15 figures (with 3 more figures in the Appendix), abstract abridged. Accepted for publication in A&A

The distribution of hot interstellar medium in early-type galaxies bears the imprint of the various astrophysical processes it underwent during its evolution. The X-ray observations of these galaxies have identified various structural features related to AGN and stellar feedback and environmental effects such as merging and sloshing. In our XMM-Newton Galaxy Atlas (NGA) project, we analyze archival observations of 38 ETGs, utilizing the high sensitivity and large field of view of XMM-Newton to construct spatially resolved 2D spectral maps of the hot gas halos. To illustrate our NGA data products in conjunction with the Chandra Galaxy Atlas (Kim et al. 2019), we describe two distinct galaxies - NGC 4636 and NGC 1550, in detail. We discuss their evolutionary history with a particular focus on the asymmetric distribution of metal-enriched, low-entropy gas caused by sloshing and AGN- driven uplift. We will release the NGA data products to a dedicated website, which users can download to perform further analyses., Comment: 19 pages, 6 figures, 2 tables. Accepted for publication in ApJS. The data-products along with the quick look results are here: https://cxc.cfa.harvard.edu/GalaxyAtlas/NGA/v1/

We present the spatial analysis of five Compton thick (CT) active galactic nuclei (AGNs), including MKN 573, NGC 1386, NGC 3393, NGC 5643, and NGC 7212, for which high resolution Chandra observations are available. For each source, we find hard X-ray emission (>3 keV) extending to ~kpc scales along the ionization cone, and for some sources, in the cross-cone region. This collection represents the first, high-signal sample of CT AGN with extended hard X-ray emission for which we can begin to build a more complete picture of this new population of AGN. We investigate the energy dependence of the extended X-ray emission, including possible dependencies on host galaxy and AGN properties, and find a correlation between the excess emission and obscuration, suggesting a connection between the nuclear obscuring material and the galactic molecular clouds. Furthermore, we find that the soft X-ray emission extends farther than the hard X-rays along the ionization cone, which may be explained by a galactocentric radial dependence on the density of molecular clouds due to the orientation of the ionization cone with respect to the galactic disk. These results are consistent with other CT AGN with observed extended hard X-ray emission (e.g., ESO 428-G014 and the Ma et al. 2020 CT AGN sample), further demonstrating the ubiquity of extended hard X-ray emission in CT AGN., Comment: 29 pages, 22 figures, 7 tables, Accepted for publication in ApJ

We present Chandra imaging and spectral observations of Seyfert 2 galaxy NGC 4388. Three extended X-ray structures around the nucleus on kpc scale are well imaged, allowing an in-depth spatially resolved study. Both the extended hard continuum and the Fe K$\alpha$ line show similar morphology, consistent with a scenario where the ionizing emission from nucleus is reprocessed by circumnuclear cold gas, resulting in a weak reflection continuum and an associated neutral Fe K$\alpha$ line. This has been seen in other Compton thick active galactic nuclei (AGN), but NGC 4388 is one of the rare cases with a lower column density ($N_{\rm H} < 1.25\times 10^{24}$ cm$^{-2}$) along the line of sight. Significant differences in equivalent width of the Fe K$\alpha$ emission line are found for the nuclear and extended regions, which could be ascribed to different column densities or scattering angles with respect to the line of sight, rather than variations in iron abundances. The north-east and west extended structures are aligned with the galactic disk and dust lane in the HST $V-H$ map, and located at the peak of molecular gas distribution. The morphology implies that the kpc-scale radio outflow may have compressed the interstellar gas and produced clumps working as the reflector to enhance line emission. Using [OIV] emission as a proxy of the AGN intrinsic luminosity, we find that both of the extended Fe K$\alpha$ emission and reflection continuum are linearly correlated with the [OIV] luminosity, indicating a connection between the AGN and the extended emission., Comment: Accepted for publication in The Astrophysical Journal. 15 pages, 11 figures, and 5 tables

The biconical radiation pattern extending from an active galactic nucleus (AGN) may strongly photoionize the circumnuclear interstellar medium (ISM) and stimulate emission from the narrow line region (NLR). Observations of the NLR may provide clues to the structure of dense material that preferentially obscures the bicone at certain angles, and may reveal the presence of processes in the ISM tied to AGN accretion and feedback. Ground-based integral field units (IFUs) may study these processes via well-understood forbidden diagnostic lines such as [O III] and [S II], but scales of $\sim10$s of pc remain challenging to spatially resolve at these wavelengths for all but the nearest AGN. We present recent narrow filter Hubble Space Telescope (HST) observations of diagnostic forbidden ([O III], [S II]) and Balmer (H$\alpha$, H$\beta$) lines in the NLR of IC 5063. This AGN's jet inclination into the plane of the galaxy provides an important laboratory for strong AGN-host interactions. We find evidence for a low-ionization loop which emits brightly in [S II] and [N II], and which may arise from plume-like hot outflows that ablate ISM from the galactic plane before escaping laterally. We also present spatially resolved Baldwin-Phillips-Terlevich diagnostic maps of the IC 5063 NLR. These maps suggest a sharp transition to lower-ionization states outside the jet path, and that such emission is dominated by $\sim10-40$ pc clumps and filamentary structure at large (>>25{\deg}) angles from the bicone axis. Such emission may arise from precursorless shocks when AGN outflows impact low-density hot plasma in the cross-cone., Comment: Accepted by ApJ. 18 pages, 8 figures. Follow-up paper to arXiv:2009.10153

On Earth near sunset, the sun may cast "crepuscular rays" such that clouds near the horizon obscure the origin of light scattered in bright rays. In principle, AGN should be able to produce similar effects. Using new Hubble Space Telescope (HST) near-infrared and optical observations, we show that the active galaxy IC 5063 contains broad radial rays extending to $\gtrsim$11 kpc from the nucleus. We argue that the bright rays may arise from dusty scattering of continuum emission from the active nucleus, while the dark rays are due to shadowing near the nucleus, possibly by a warped torus. We also consider alternative AGN-related and stellar origins for the extended light., Comment: Accepted for publication to ApJ Letters. 13 pages, 5 figures. Facilitated by Twitter discussion (see https://twitter.com/SpaceGeck/status/1201350966945017856). This version corrects figure labels and includes other more minor updates

We present spatially resolved BPT mapping of the extended narrow line regions (ENLRs) of seven nearby Seyfert 2 galaxies, using HST narrow band filter imaging. We construct the BPT diagrams using $\leq$ 0.1" resolution emission line images of [O III]$\lambda$5007, H$\alpha$, [S II]$\lambda$$\lambda$6717,6731, and H$\beta$. By mapping these diagnostic lines according to the BPT classification, we dissect the ENLR into Seyfert, LINER, and star-forming regions. The nucleus and ionization cones are dominated by Seyfert-type emission, which can be interpreted as predominantly photoionization by the active galactic nucleus (AGN). The Seyfert nucleus and ionization cones transition to and are surrounded by a LINER cocoon, extending up to $\sim$ 250 pc in thickness. The ubiquity of the LINER cocoon in Seyfert 2 galaxies suggests that the circumnuclear regions are not necessarily Seyfert-type, and LINER activity plays an important role in Seyfert 2 galaxies. We demonstrate that spatially resolved diagnostics are crucial to understanding the excitation mechanisms in different regions and the AGN-host galaxy interactions., Comment: 19 pages, 14 figures; accepted for publication in ApJ

We present a reanalysis of the cumulative ACIS S Chandra data set pointed at the double AGNs of the NGC 6240 merging galaxy, focusing on the hard energy bands containing the hard spectral continuum (5.5-5.9 keV), the redshifted Fe I K alpha line (6.0-6.4 keV), and the redshifted Fe XXV line (6.4-6.7 keV). We have used to the full the Chandra telescope angular resolution, and we have modeled the Chandra PSF by comparing pre-flight calibration model to the data for the two bright AGNs. With two complementary approaches: (1) studying the residuals after PSF subtraction, and (2) producing reconstructed Expectation through Markov Chain Monte Carlo (EMC2) images, we are able to resolve structures extending from 1 kpc to <200 pc in the S AGN. The latter are within the sphere of influence of this BH. We find significant extended emission in both continuum and Fe lines in the 2'' (1 kpc) region surrounding the nuclei, in the region between the N and S AGN, and in a sector of PA 120-210 deg. extending to the SE from the centroid of the S AGN surface brightness. The extended Fe I K alpha emission is likely to originate from fluorescence of X-ray photons interacting with dense molecular clouds, providing a complementary view to recent high-resolution ALMA studies. The non-thermal emission is more prevalent in the region in between the two active X-ray nuclei, and in the N AGN. We do not find strong evidence of X-ray emission associated with the 3rd nucleus recently proposed for NGC 6240., Comment: in press on The Astrophysical Journal

We present a new catalogue of ~2,400 optically selected quasars with spectroscopic redshifts and X-ray observations from either Chandra or XMM-Newton. The sample can be used to investigate the non-linear relation between the UV and X-ray luminosity of quasars, and to build a Hubble diagram up to redshift z~7.5. We selected sources that are neither reddened by dust in the optical/UV nor obscured by gas in the X-rays, and whose X-ray fluxes are free from flux-limit related biases. After checking for any possible systematics, we confirm, in agreement with our previous works, that (i) the X-ray to UV relation provides distance estimates matching those from supernovae up to z~1.5, and (ii) its slope shows no redshift evolution up to z~5. We provide a full description of the methodology for testing cosmological models, further supporting a trend whereby the Hubble diagram of quasars is well reproduced by the standard flat $\Lambda$CDM model up to z~1.5-2, but strong deviations emerge at higher redshifts. Since we have minimized all non-negligible systematic effects, and proven the stability of the $L_{\rm X}-L_{\rm UV}$ relation at high redshifts, we conclude that an evolution of the expansion rate of the Universe should be considered as a possible explanation for the observed deviation, rather than some systematic (redshift-dependent) effect associated with high-redshift quasars., Comment: 24 pages, 17 figures, accepted for publication in A&A

The recent Chandra discovery of extended $\sim$kpc-scale hard ($>$ 3 keV) X-ray emission in nearby Compton-thick (CT) active galactic nuclei (AGN) opens a new window to improving AGN torus modeling and investigating how the central super massive black hole interacts with and impacts the host galaxy. Since there are only a handful of detections so far, we need to establish a statistical sample to determine the ubiquity of the extended hard X-ray emission in CT AGN, and quantify the amount and extent of this component. In this paper, we present the spatial analysis results of a pilot Chandra imaging survey of 7 nearby ($0.006 < z < 0.013$) CT AGN selected from the Swift-BAT spectroscopic AGN survey. We find that five out of the seven CT AGN show extended emission in the 3-7 keV band detected at $>$ 3$\sigma$ above the Chandra PSF with $\sim$12% to 22% of the total emission in the extended components. ESO 137-G034 and NGC 3281 display biconical ionization structures with extended hard X-ray emission reaching kpc-scales ($\sim$ 1.9 kpc and 3.5 kpc in diameter). The other three show extended hard X-ray emission above the PSF out to at least $\sim$360 pc in radius. We find a trend that a minimum 3-7 keV count rate of 0.01 cts/s and total excess fraction $>$20% is required to detect a prominent extended hard X-ray component. Given that this extended hard X-ray component appears to be relatively common in this uniformly selected CT AGN sample, we further discuss the implications for torus modeling and AGN feedback., Comment: 20 pages, 20 figures, accepted for publication in ApJ

X-ray binaries exhibit a wide range of properties but there are few accepted methods to determine the nature of the compact object. Color-Color-Intensity diagrams have been suggested as a means of distinguishing between systems containing black holes from those containing neutron stars. However, this technique has been verified with data from only one instrument (RXTE/ASM) with a single set of X-ray colors defined using data available only in pre-determined energy bands. We test a selection of X-ray colors with a more sensitive instrument to determine the reliability of this method. We use data from the MAXI Gas Slit Camera, which allows users to specify energy-bands. We test X-ray colors that have been previously defined in the literature as well as ones that we define specifically in this paper. A representative set of systems are used to construct Color-Color-Intensity diagrams in each set of colors to determine which are best for separating different classes. For studying individual sources certain bands are more effective than others. For a specified energy range, the separation of soft states in black hole binaries was possible only where both soft and hard colors included information from the lowest energy band. We confirm that Color-Color-Intensity diagrams can distinguish between systems containing black holes or neutron stars in all X-ray colors tested; this suggests an universality in the accretion processes governing these different classes. We suggest possible physical processes driving different classes of X-ray binaries to different locations in Color-Color-Intensity diagrams., Comment: 23 pages, 19 figures. Accepted in New Astronomy

Recent observations of nearby Compton thick (CT) active galactic nuclei (AGNs) with Chandra have resolved hard (>3 keV) X-ray emission extending out from the central supermassive black hole to kiloparsec scales, challenging the long-held belief that the characteristic hard X-ray continuum and fluorescent Fe K lines originate in the inner ~parsec due to the excitation of obscuring material. In this paper we present the results of the most recent Chandra ACIS-S observations of NGC 7212, a CT AGN in a compact group of interacting galaxies, with a total effective exposure of ~150 ks. We find ~20 percent of the observed emission is found outside of the central ~kiloparsec, with ~17 percent associated with the soft X-rays, and ~3 percent with hard X-ray continuum and Fe K line. This emission is extended both along the ionization cone and in the cross-cone direction up to ~3.8 kpc scales. The spectrum of NGC 7212 is best represented by a mixture of thermal and photoionization models that indicate the presence of complex gas interactions. These observations are consistent with what is observed in other CT AGN (e.g., ESO 428-G014, NGC 1068), providing further evidence that this may be a common phenomenon. High-resolution observations of extended CT AGN provide an especially valuable environment for understanding how AGN feedback impacts host galaxies on galactic scales., Comment: 20 pages, 10 figures, 8 tables, Accepted for publication in ApJ