- ID:
- ivo://CDS.VizieR/J/ApJ/865/43
- Title:
- X-ray stacking analysis of Chandra-COSMOS gal.
- Short Name:
- J/ApJ/865/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an X-ray stacking analysis of ~75000 star-forming galaxies between 0.1<z<5.0 using the Chandra COSMOS-Legacy survey to study the X-ray emission of low-luminosity active galactic nuclei (AGN) and its connection to host galaxy properties. The stacks at z<0.9 have luminosity limits as low as 10^40^-10^41^erg/s, a regime in which X-ray binaries (XRBs) can dominate the X-ray emission. Comparing the measured luminosities to established XRB scaling relations, we find that the redshift evolution of the luminosity per star formation rate (SFR) of XRBs depends sensitively on the assumed obscuration and may be weaker than previously found. The XRB scaling relation based on stacks from the Chandra Deep Field South overestimates the XRB contribution to the COSMOS high specific SFR stacks, possibly due to a bias affecting the CDF-S stacks because of their small galaxy samples. After subtracting the estimated XRB contribution from the stacks, we find that most stacks at z>1.3 exhibit a significant X-ray excess indicating nuclear emission. The AGN emission is strongly correlated with stellar mass but does not exhibit an additional correlation with SFR. The hardness ratios of the high-redshift stacks indicate that the AGN are substantially obscured (N_H_~10^23^cm^-2^). These obscured AGN are not identified by IRAC color selection and have L_X_~10^41^-10^43^erg/s, consistent with accretion at an Eddington rate of ~10^-3^ onto 10^7^-10^8^M_{sun}_ black holes. Combining our results with other X-ray studies suggests that AGN obscuration depends on stellar mass and an additional variable, possibly the Eddington rate.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/440/269
- Title:
- X-ray survey of the 2Jy sample. I.
- Short Name:
- J/MNRAS/440/269
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carry out a systematic study of the X-ray emission from the active nuclei of the 0.02<z<0.7 2Jy sample, using Chandra and XMM-Newton observations. We combine our results with those from mid-infrared, optical emission-line and radio observations, and add them to those of the 3CRR sources. We show that the low-excitation objects in our samples show signs of radiatively inefficient accretion. We study the effect of the jet-related emission on the various luminosities, confirming that it is the main source of soft X-ray emission for our sources. We also find strong correlations between the accretion-related luminosities, and identify several sources whose optical classification is incompatible with their accretion properties. We derive the bolometric and jet kinetic luminosities for the samples and find a difference in the total Eddington rate between the low- and high-excitation populations, with the former peaking at ~1% and the latter at ~20% Eddington. Our results are consistent with a simple Eddington switch when the effects of environment on radio luminosity and black hole mass calculations are considered. The apparent independence of jet kinetic power and radiative luminosity in the high-excitation population in our plots supports a model in which jet production and radiatively efficient accretion are not strongly correlated in high-excitation objects, though they have a common underlying mechanism.
- ID:
- ivo://CDS.VizieR/J/ApJ/788/48
- Title:
- X-ray through NIR photometry of NGC 2617
- Short Name:
- J/ApJ/788/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- After the All-Sky Automated Survey for SuperNovae discovered a significant brightening of the inner region of NGC 2617, we began a ~70 day photometric and spectroscopic monitoring campaign from the X-ray through near-infrared (NIR) wavelengths. We report that NGC 2617 went through a dramatic outburst, during which its X-ray flux increased by over an order of magnitude followed by an increase of its optical/ultraviolet (UV) continuum flux by almost an order of magnitude. NGC 2617, classified as a Seyfert 1.8 galaxy in 2003, is now a Seyfert 1 due to the appearance of broad optical emission lines and a continuum blue bump. Such "changing look active galactic nuclei (AGNs)" are rare and provide us with important insights about AGN physics. Based on the H{beta} line width and the radius-luminosity relation, we estimate the mass of central black hole (BH) to be (4+/-1)x10^7^ M_{sun}_. When we cross-correlate the light curves, we find that the disk emission lags the X-rays, with the lag becoming longer as we move from the UV (2-3 days) to the NIR (6-9 days). Also, the NIR is more heavily temporally smoothed than the UV. This can largely be explained by a simple model of a thermally emitting thin disk around a BH of the estimated mass that is illuminated by the observed, variable X-ray fluxes.
- ID:
- ivo://CDS.VizieR/J/ApJS/177/465
- Title:
- X-ray variability in NGC 6946, NGC 4485/90
- Short Name:
- J/ApJS/177/465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze data from five Chandra observations of the spiral galaxy NGC 6946 and from three Chandra observations of the irregular/spiral interacting galaxy pair NGC 4485/4490, with an emphasis on investigating the long-term variability exhibited by the source populations. We detect 90 point sources coincident with NGC 6946 down to luminosities of a few times 10^36^ergs/s, and 38 sources coincident with NGC 4485/90 down to a luminosity of ~1x10^37^ergs/s. Twenty-five (15) sources in NGC 6946 (NGC 4485/90) exhibit long-term (i.e., weeks to years) variability in luminosity; 11 (4) are transient candidates. The single ultraluminous X-ray source (ULX) in NGC 6946 and all but one of the eight ULXs in NGC 4485/90 exhibit long-term flux variability. Two of the ULXs in NGC 4485/90 have not been identified before as ultraluminous sources. The widespread variability in both systems is indicative of the populations being dominated by X-ray binaries, and this is supported by the X-ray colors of the sources. The distribution of colors among the sources indicates a large fraction of high-mass X-ray binaries in both systems. The shapes of the X-ray luminosity functions of the galaxies do not change significantly between observations and can be described by power laws with cumulative slopes ~0.6-0.7 (NGC 6946) and ~0.4 (NGC 4485/90).
- ID:
- ivo://CDS.VizieR/J/AJ/139/1066
- Title:
- X-ray view of NGC 2403 central region
- Short Name:
- J/AJ/139/1066
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Archival Chandra observations are used to study the X-ray emission associated with star formation in the central region of the nearby SAB(s)cd galaxy NGC 2403. The distribution of X-ray emission is compared to the morphology visible at other wavelengths using complementary Spitzer, Galaxy Evolution Explorer, and ground-based H{alpha} imagery.
- ID:
- ivo://CDS.VizieR/J/ApJS/245/17
- Title:
- X-shaped radio galaxies from FIRST
- Short Name:
- J/ApJS/245/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 290 "winged" or X-shaped radio galaxies (XRGs) extracted from the latest (2014 December 17) data release of the "Very Large Array Faint Images of the Radio Sky at Twenty centimeter". We have combined these radio images with their counterparts in the TIFR GMRT sky survey at 150MHz, in an attempt to identify any low surface brightness radio emission present in these sources. This has enabled us to assemble a sample of 106 "strong" XRG candidates and 184 "probable" XRG candidates whose XRG designation needs to be verified by further observations. The present sample of 290 XRG candidates is almost twice as large as the number of XRGs currently known. Twenty-five of our 290 XRG candidates (9 "strong" and 16 "probable") are identified as quasars. Double-peaked narrow emission lines are seen in the optical spectra of three of the XRG candidates (two "strong" and one "probable"). Nearly 90% of the sample is located in the FR II domain of the Owen-Ledlow diagram. A few of the strong XRG candidates have a rather flat radio spectrum (spectral index {alpha} flatter than -0.3) between 150MHz and 1.4GHz, or between 1.4 and 5GHz. Since this is not expected for lobe-dominated extragalactic radio sources (like nearly all known XRGs), these sources are particularly suited for follow-up radio imaging and near-simultaneous measurement of the radio spectrum.
- ID:
- ivo://CDS.VizieR/J/ApJS/181/548
- Title:
- X-shaped radio sources. II. New redshifts
- Short Name:
- J/ApJS/181/548
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We reported optical spectroscopic observations of X-shaped radio sources with the Hobby-Eberly Telescope and Multiple-Mirror Telescope, focused on the sample of candidates from the FIRST survey presented in Paper I (Cheung, 2007, Cat. <J/AJ/133/2097>). A total of 27 redshifts were successfully obtained, 21 of which are new, including a newly identified candidate source of this type which is presented here. With these observations, the sample of candidates from the previous paper is over 50% spectroscopically identified. Two new broad emission-lined X-shaped radio sources are revealed, while no emission lines were detected in about one-third of the observed sources; a detailed study of the line properties is deferred to a future paper. Finally, to explore their relation to the Fanaroff-Riley division, the radio luminosities and host galaxy absolute magnitudes of a spectroscopically identified sample of 50 X-shaped radio galaxies are calculated to determine their placement in the Owen-Ledlow plane.
- ID:
- ivo://CDS.VizieR/J/ApJ/852/48
- Title:
- "X-shaped" radio sources. II. Sample properties
- Short Name:
- J/ApJ/852/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In an earlier paper, we presented Jansky Very Large Array multi-frequency, multi-array continuum imaging of a unique sample of low-axial ratio radio galaxies. In this paper, the second in the series, we examine the images to learn the phenomenology of how the off-axis emission relates to the main radio source. Inversion-symmetric offset emission appears to be bimodal and to originate from one of two strategic locations: outer ends of radio lobes (outer-deviation) or from inner ends (inner-deviation). The latter sources are almost always associated with edge-brightened sources. With S- and Z-shaped sources being a subset of outer-deviation sources, this class lends itself naturally to explanations involving black hole axis precession. Our data allow us to present a plausible model for the more enigmatic inner-deviation sources with impressive wings; as for outer-deviation sources these too require black hole axis shifts, although they also require plasma backflows into relic channels. Evolution in morphology over time relates the variety in structures in inner-deviation sources including XRGs. With features such as non- collinearities, central inner-S "spine," corresponding lobe emission peaks, double and protruding hotspots not uncommon, black hole axis precession, drifts, or flips could be active in a significant fraction of radio sources with prominent off-axis emission. At least 4% of radio galaxies appear to undergo black hole axis rotation. Quasars offer a key signature for recognizing rotating axes. With a rich haul of sources that have likely undergone axis rotation, our work shows the usefulness of low-axial ratio sources in pursuing searches for binary supermassive black holes.
- ID:
- ivo://CDS.VizieR/J/ApJ/852/47
- Title:
- "X-shaped" radio sources. I. VLA imaging
- Short Name:
- J/ApJ/852/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present archival and Jansky Very Large Array multi-frequency multi-array radio continuum imaging of a unique sample of 100 radio sources that have been selected to be candidate "X-shaped" radio galaxies (XRGs). The archival data were calibrated in AIPS (Bridle & Greisen 1994, NRAO AIPS Memo 87) and imaged using DIFMAP (Shepherd+ 1994BAAS...26..987S), while the new Very Large Array data were calibrated and imaged in CASA (McMullin+ 2007ASPC..376..127M). No attempt was made to re-image the archival data in CASA. Altogether we present images of 95 of the 100 sources. These observations give us the opportunity to study radio sources with synchrotron plasma that is significantly offset from the main radio axis and therefore to open a window into investigations of physical mechanisms responsible for depositing the plasma in off-axis regions. Here, we present the technical details of the observations and all of the total intensity images, while in subsequent papers we use them to examine critically various models for the formation of XRGs. Spectral index and linear polarization information is also presented and analyzed in further papers in this series.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A1
- Title:
- X-shooter spectra of 6 ~2.2 quasars
- Short Name:
- J/A+A/603/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We studied the spectra of six z~2.2 quasars obtained with the X-shooter spectrograph at the Very Large Telescope. The redshift of these sources and X-shooter's spectral coverage allow us to cover the rest spectral range ~1200-7000{AA} for the simultaneous detection of optical and ultraviolet lines emitted by the Broad Line Region. Simultaneous measurements, avoiding issues related to quasars variability, help us understanding the connection between different Broad Line Region line profiles generally used as virial estimators of Black Holes masses in quasars. The goal of this work is comparing the emission lines from the same object to check on the reliability of H{alpha}, MgII and CIV with respect to H{beta}. H{alpha} and MgII linewidths correlate well with H{beta}, while CIV shows a poorer correlation, due to the presence of strong blueshifts and asymmetries in the profile. We compare our sample with the only other two whose spectra were taken with the same instrument and for all examined lines our results are in agreement with the ones obtained with X-shooter at z~1.5-1.7. We finally evaluate CIII] as a possible substitute of CIV in the same spectral range and find that its behaviour is more coherent with those of the other lines: we believe that, when a high quality spectrum such as the ones we present is available and a proper modelization with the FeII and FeIII emissions is performed, the use of this line is more appropriate than that of CIV if not corrected for the contamination by non-virialized components.
