- ID:
- ivo://CDS.VizieR/J/ApJ/869/171
- Title:
- Chandra observations of NuSTAR sources
- Short Name:
- J/ApJ/869/171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Nuclear Spectroscopic Telescope Array (NuSTAR) serendipitous survey has already uncovered a large number of active galactic nuclei (AGNs), providing new information about the composition of the cosmic X-ray background. For AGNs off the Galactic plane, it has been possible to use existing X-ray archival data to improve source localizations, identify optical counterparts, and classify the AGNs with optical spectroscopy. However, near the Galactic plane, better X-ray positions are necessary to achieve optical or near-IR identifications due to the higher levels of source crowding. Thus, we have used observations with the Chandra X-ray Observatory to obtain the best possible X-ray positions. With eight observations, we have obtained coverage for 19 NuSTAR serendips within 12{deg} of the plane. One or two Chandra sources are detected within the error circle of 15 of the serendips, and we report on these sources and search for optical counterparts. For one source (NuSTAR J202421+3350.9), we obtained a new optical spectrum and detected the presence of hydrogen emission lines. The source is Galactic, and we argue that it is likely a cataclysmic variable. For the other sources, the Chandra positions will enable future classifications in order to place limits on faint Galactic populations, including high-mass X-ray binaries and magnetars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/900/79
- Title:
- Chandra obs. of SDSS AGN pairs at z_med_~0.1
- Short Name:
- J/ApJ/900/79
- Date:
- 21 Mar 2022 09:29:38
- Publisher:
- CDS
- Description:
- We present a Chandra archival study of optically selected active galactic nucleus (AGN) pairs at a median redshift z~0.1. Out of 1286 AGN pairs (with projected separations rp<100kpc and velocity offsets {Delta}v<600km/s) optically identified from the Sloan Digital Sky Survey Seventh Data Release, we find 67 systems with archival Chandra observations, which represents the largest sample of optically selected AGN pairs studied in the X-ray. Among the 67 AGN pairs, 21 systems have both nuclei detected in the X-ray, 36 have one nucleus detected in the X-ray, and 10 have no X-ray detection. The X-ray detection rate, 78/134=58% (+/-7% 1{sigma} Poisson errors), is significantly higher than that (23/134=17%+/-4%) of a comparison sample of star-forming galaxy pairs, lending support to the optical AGN classification. In the conservative case where X-ray contamination from star formation is removed, the X-ray detection rate becomes 27%+/-4%, consistent with predictions from the latest galaxy merger simulations. The 2-10keV X-ray luminosity L2-10keV increases with decreasing projected separation in AGN pairs for rp>~15kpc, suggesting an enhancement of black hole accretion even in early-stage mergers. On the other hand, L2-10keV appears to decrease with decreasing projected separation at rp<~15kpc, which is contradictory to predictions from merger simulations. The apparent decrease in L2-10 keV of AGN pairs at rp<~15kpc may be caused by (i) enhanced absorbing columns from merger-induced gas inflows, (ii) feedback effects from early-stage mergers, and/or (iii) small number statistics. Future X-ray studies with larger samples are needed to put our results on firmer statistical ground.
- ID:
- ivo://CDS.VizieR/J/ApJS/168/19
- Title:
- Chandra sources in 5 galaxy clusters
- Short Name:
- J/ApJS/168/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present catalogs and images of optical counterparts to the Chandra-selected X-ray sources found in the fields of the five clusters RX J0152-1357, RX J0849+4452, RDCS J0910+5422, MS 1054-0321, and RDCS J1252-2927, which were imaged with the Advanced Camera for Surveys as part of the ACS Guaranteed Time Observer programs. A total of 98 X-ray sources fall within the ACS mosaics, and positive identifications are made for ~96% of them, including confirmed cluster members. We classify the sources as active galactic nuclei (AGNs) or QSOs depending on their X-ray output.
- ID:
- ivo://CDS.VizieR/J/ApJ/648/111
- Title:
- Chandra sources near AGNs
- Short Name:
- J/ApJ/648/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze observations obtained with the Chandra X-Ray Observatory of bright Compton-thick active galactic nuclei (AGNs), those with column densities in excess of 1.5x10^24^cm^-2^ along the lines of sight. We therefore view the powerful central engines only indirectly, even at X-ray energies. Using high spatial resolution and considering only galaxies that do not contain circumnuclear starbursts, we reveal the variety of emission AGNs alone may produce.
- ID:
- ivo://CDS.VizieR/J/A+A/655/A109
- Title:
- Chandra view of the LX-LUV relation in quasars
- Short Name:
- J/A+A/655/A109
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- 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 (2332 quasars) and the Chandra COSMOS Legacy survey (273 quasars). The non-linear relation between the ultraviolet (at 2500{AA}, LUV) and the X-ray (at 2keV, LX) 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. 3430 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 LX-LUV relation exists by dividing the sample in narrow redshift intervals across the redshift range spanned by our sample, z~=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.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/171
- Title:
- [CII]158um line fluxes of AGN from Herschel
- Short Name:
- J/ApJ/755/171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Results are presented for [CII] 158{mu}m line fluxes observed with the Herschel PACS instrument in 112 sources with both starburst and active galactic nucleus (AGN) classifications, of which 102 sources have confident detections. Results are compared with mid-infrared spectra from the Spitzer Infrared Spectrometer and with L_ir_ from IRAS fluxes; AGN/starburst classifications are determined from equivalent width of the 6.2{mu}m polycyclic aromatic hydrocarbon (PAH) feature. It is found that the [CII] line flux correlates closely with the flux of the 11.3{mu}m PAH feature independent of AGN/starburst classification, log[f([CII]158{mu}m)/f(11.3{mu}mPAH)]=-0.22+/-0.25. It is concluded that the [CII] line flux measures the photodissociation region associated with starbursts in the same fashion as the PAH feature. A calibration of star formation rate (SFR) for the starburst component in any source having [CII] is derived comparing [CII] luminosity L([CII]) to L_ir_ with the result that logSFR=logL([CII)])-7.08+/-0.3, for SFR in M_{sun}_/yr and L([CII]) in L_{sun}_. The decreasing ratio of L([CII]) to L_ir_ in more luminous sources (the "[CII] deficit") is shown to be a consequence of the dominant contribution to L_ir_arising from a luminous AGN component because the sources with the largest L_ir_ and smallest L([CII])/L_ir_ are AGNs.
- ID:
- ivo://CDS.VizieR/J/A+A/639/L13
- Title:
- 4C 41.17 IRAM/NOEMA data cubes
- Short Name:
- J/A+A/639/L13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new, spatially resolved [CI]1-0, [CI]2-1, CO(7-6), and dust continuum observations of 4C 41.17 at z=3.8. This is one of the best-studied radio galaxies in this epoch and is arguably the best candidate of jet-triggered star formation at high redshift currently known in the literature. 4C 41.17 shows a narrow ridge of dust continuum extending over 15kpc near the radio jet axis. Line emission is found within the galaxy in the region with signatures of positive feedback. Using the [CI]1-0 line as a molecular gas tracer, and multifrequency observations of the far-infrared dust heated by star formation, we find a total gas mass of 7.6x10^10^M_{sun}_, which is somewhat greater than that previously found from CO(4-3). The gas mass surface density of 10^3^M_{sun}_/yr/pc^2^ and the star formation rate surface density of 10M_{sun}_/yr/kpc^2^ were derived over the 12 kpc8 kpc area, where signatures of positive feedback have previously been found. These densities are comparable to those in other populations of massive, dusty star-forming galaxies in this redshift range, suggesting that the jet does not currently enhance the efficiency with which stars form from the gas. This is consistent with expectations from simulations, whereby radio jets may facilitate the onset of star formation in galaxies without boosting its efficiency over longer timescales, in particular after the jet has broken out of the interstellar medium, as is the case in 4C 41.17. The release includes Gaussian line fits to the [CI]1-0, [CI]2-1, and CO(7-6) emission lines in the radio galaxy 4C 41.17 at z=3.8, as well as the interferometric data cubes.
- ID:
- ivo://CDS.VizieR/J/A+A/549/A139
- Title:
- Circinus galaxy CRIRES observations
- Short Name:
- J/A+A/549/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new CRIRES spectroscopic observations of the Br{gamma} emission line in the nuclear region of the Circinus galaxy, obtained with the aim of measuring the black hole (BH) mass with the spectroastrometric technique. The Circinus galaxy is an ideal benchmark for the spectroastrometric technique given its proximity and secure BH measurement obtained with the observation of its nuclear H_2_O maser disk. The kinematical data have been analyzed both with the classical method based on the analysis of the rotation curves and with the new method developed by us that is based on spectroastrometry. The classical method indicates that the gas disk rotates in a gravitational potential resulting from an extended stellar mass distribution and a spatially unresolved dynamical mass of (1.7+/-0.2)x10^7^M_{sun}_, concentrated within r<7pc, corresponding to the seeing-limited resolution of the observations. The new method is capable of probing the gas rotation at scales that are a factor ~3.5 smaller than those probed by the rotation curve analysis, highlighting the potential of spectroastrometry. The dynamical mass, which is spatially unresolved with the spectroastrometric method, is a factor ~2 smaller, 7.9^+1.4^_-1.1_x10^6^M_{sun}_, indicating that spectroastrometry has been able to spatially resolve the nuclear mass distribution down to 2 pc scales. This unresolved mass is still a factor ~4.5 larger than the BH mass measurement obtained with the H_2_O maser emission, indicating that even with spectroastrometry, it has not been possible to resolve the sphere of influence of the BH. Based on literature data, this spatially unresolved dynamical mass distribution is likely dominated by warm molecular gas and has been tentatively identified with the circum-nuclear torus that prevents a direct view of the central BH in Circinus. This mass distribution, with a size of ~2pc, is similar in shape to that of the star cluster of the Milky Way, suggesting that a molecular torus, forming stars at a high rate, might be the earlier evolutionary stage of the nuclear star clusters that are common in late-type spirals.
- ID:
- ivo://CDS.VizieR/J/AJ/131/1262
- Title:
- Circular polarization images at 15GHz of AGN jets
- Short Name:
- J/AJ/131/1262
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report first-epoch circular polarization results for 133 active galactic nuclei in the MOJAVE (Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments) program to monitor the structure and polarization of a flux-limited sample of extragalactic radio jets with the VLBA at 15GHz. We found strong circular polarization (0.3%) in approximately 15% of our sample. The circular polarization was usually associated with jet cores; however, we did find a few strong jet components to be circularly polarized.
- ID:
- ivo://CDS.VizieR/J/ApJS/146/353
- Title:
- Circumnuclear dust in galaxies
- Short Name:
- J/ApJS/146/353
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The detailed morphology of the interstellar medium (ISM) in the central kiloparsec of galaxies is controlled by pressure and gravitation. The combination of these forces shapes both circumnuclear star formation and the growth of the central, supermassive black hole. We present visible and near-infrared Hubble Space Telescope images and color maps of 123 nearby galaxies that show the distribution of the cold ISM, as traced by dust, with excellent spatial resolution. These observations reveal that nuclear dust spirals are found in the majority of active and inactive galaxies and they possess a wide range in coherence, symmetry, and pitch angle. We have used this large sample to develop a classification system for circumnuclear dust structures.
