- ID:
- ivo://CDS.VizieR/J/MNRAS/440/799
- Title:
- Low Ionization BALQSOs MgII and AlIII variability
- Short Name:
- J/MNRAS/440/799
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of our time variability studies of MgII and AlIII absorption lines in a sample of 22 Low Ionization Broad Absorption Line QSOs (LoBAL QSOs) at 0.2<=z_em_<=2.1 using the 2-m telescope at IUCAA Girawali Observatory over a time-scale of 10d to 7.69years in the QSO's rest frame. Spectra are analysed in conjunction with photometric light curves from Catalina Real-Time Transient Survey. Long time-scale (i.e. >=1-year) absorption line variability is seen in eight cases (36 per cent systems) while only four of them (i.e. 18 per cent systems) show variability over short time-scales (i.e. <1-year). We notice a tendency of highly variable LoBAL QSOs to have high ejection velocity, low equivalent width and low redshift. The detection rate of variability in LoBAL QSOs showing Fe fine-structure lines (FeLoBAL QSOs) is less than that seen in non-Fe LoBAL QSOs. Absorption line variability is more frequently detected in QSOs having continuum dominated by Fe emission lines compared to rest of the QSOs. Confirming these trends with a bigger sample will give vital clues for understanding the physical distinction between different BAL QSO sub-classes. We correlate the absorption line variability with various parameters derived from continuum light curves and find no clear correlation between continuum flux and absorption line variabilities. However, sources with large absorption line variability also show large variability in their light curves. We also see appearance/disappearance of absorption components in two cases and clear indications for profile variations in four cases. The observed variability can be best explained by a combination of process driven by continuum variations and clouds transiting across the line of sight.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/997
- Title:
- Low-luminosity radio-loud AGN
- Short Name:
- J/MNRAS/465/997
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HI absorption studies of active galaxies enable us to probe their circumnuclear regions and the general interstellar medium and study the supply of gas that may trigger nuclear activity. In this article, we investigate the dependence of the detection rate of HI absorption on the nature of radio galaxies based on their emission-line spectra and on the nature of host galaxies based on WISE colours and their radio structure, which may help us understand the different accretion modes. We find significant differences in the distributions of W2-W3 colour for sources with HI absorption detections and non-detections. We report a high detection rate of HI absorption in those galaxies with WISE infrared colours W2-W3>2, typical of gas-rich systems, along with a compact radio structure. The HI detection rate for low-excitation radio galaxies (LERGs) with W2-W3>2 and compact radio structure is high (70.6+/-20.4 per cent). In high-excitation radio galaxies (HERGs), compact radio structure in the nuclear or circumnuclear region could give rise to absorption by gas in the dusty torus, in addition to gas in the interstellar medium. However, the higher specific star-formation rate (sSFR) for LERGs with W2-W3>2 suggests that HI absorption may be largely due to star-forming gas in their hosts. LERGs with extended radio structure tend to have significantly lower values of W2-W3 compared with those with compact structure. Extended radio sources and those with W2-W3<2 have low HI detection rates.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A138
- Title:
- Low-luminosity type-1 QSO sample. V.
- Short Name:
- J/A+A/587/A138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near-infrared (NIR) H+K-band long-slit spectra of eleven galaxies that were obtained with SOFI at the NTT (ESO). The galaxies are chosen from the low-luminosity type-1 quasi-stellar object (LLQSO) sample, which comprises the 99 closest (z<=0.06) QSOs from the Hamburg/ESO survey for bright UV-excess QSOs. These objects are ideal targets to study the gap between local Seyfert galaxies and high-redshift quasars because they show much stronger AGN activity than local objects, but are still close enough for a detailed structural analysis. We fit hydrogen recombination, molecular hydrogen, and [FeII] lines after carefully subtracting the continuum emission. From the broad Pa{alpha} components, we estimated black hole masses and enlarged the sample of LLQSOs that deviate from the MBH-Lbulge relations of inactive galaxies from 12 to 16 objects. All objects show emission from hot dust (T~1200K) as well as stellar contribution. However, the respective fractions vary strongly among the objects. More than half of the objects show H_2_ emission lines, which indicate a large reservoir of molecular gas that is needed to feed the AGN and star formation. In the NIR diagnostic diagram all objects lie in the location of AGN-dominated objects. However, most of the objects show indications of star formation activity, suggesting that their offset location with respect to MBH-Lbulge relations of inactive galaxies may be a consequence of overluminous bulges.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/167
- Title:
- Low-mass black holes in SDSS Seyfert 1 galaxies
- Short Name:
- J/ApJ/755/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a systematic search of low-mass black holes (BHs) in active galactic nuclei (AGNs) with broad H{alpha} emission lines, aiming at building a homogeneous sample that is more complete than previous ones for fainter, less highly accreting sources. For this purpose, we developed a set of elaborate, automated selection procedures and applied it uniformly to the Fourth Data Release of the Sloan Digital Sky Survey. Special attention is given to AGN-galaxy spectral decomposition and emission-line deblending. We define a sample of 309 type 1 AGNs with BH masses in the range 8x10^4^-2x10^6^M_{sun}_ (with a median of 1.2x10^6^M_{sun}_), using the virial mass estimator based on the broad H{alpha} line. About half of our sample of low-mass BHs differs from that of Greene & Ho (2007, Cat. J/ApJ/670/92), with 61 of them discovered here for the first time. Our new sample picks up more AGNs with low accretion rates: the Eddington ratios of the present sample range from <~0.01 to ~1, with 30% below 0.1. This suggests that a significant fraction of low-mass BHs in the local universe are accreting at low rates. The host galaxies of the low-mass BHs have luminosities similar to those of L* field galaxies, optical colors of Sbc spirals, and stellar spectral features consistent with a continuous star formation history with a mean stellar age of less than 1Gyr.
- ID:
- ivo://CDS.VizieR/J/ApJS/235/40
- Title:
- Low-mass black holes in Sy1 galaxies. II. SDSS-DR7
- Short Name:
- J/ApJS/235/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new sample of 204 low-mass black holes (LMBHs) in active galactic nuclei (AGNs) is presented with black hole masses in the range of (1-20)x10^5^M_{sun}_. The AGNs are selected through a systematic search among galaxies in the Seventh Data Release (DR7) of the Sloan Digital Sky Survey (SDSS), and careful analyses of their optical spectra and precise measurement of spectral parameters. Combining them with our previous sample selected from SDSS DR4 makes it the largest LMBH sample so far, totaling over 500 objects. Some of the statistical properties of the combined LMBH AGN sample are briefly discussed in the context of exploring the low-mass end of the AGN population. Their X-ray luminosities follow the extension of the previously known correlation with the [OIII] luminosity. The effective optical-to-X-ray spectral indices {alpha}_OX_, albeit with a large scatter, are broadly consistent with the extension of the relation with the near-UV luminosity L_2500{AA}_. Interestingly, a correlation of {alpha}_OX_ with black hole mass is also found, with {alpha}OX being statistically flatter (stronger X-ray relative to optical) for lower black hole masses. Only 26 objects, mostly radio loud, were detected in radio at 20cm in the FIRST survey, giving a radio-loud fraction of 4%. The host galaxies of LMBHs have stellar masses in the range of 10^8.8^-10^12.4^M_{sun}_ and optical colors typical of Sbc spirals. They are dominated by young stellar populations that seem to have undergone continuous star formation history.
- ID:
- ivo://CDS.VizieR/J/ApJ/684/654
- Title:
- Low-mass members of Chamaeleon I
- Short Name:
- J/ApJ/684/654
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used images obtained with the Infrared Array Camera and the Multiband Imaging Photometer on board the Spitzer Space Telescope to search for low-mass stars and brown dwarfs with circumstellar disks in the Chamaeleon I star-forming region. Through optical spectroscopy of sources with red colors in these data, we have identified seven new disk-bearing members of the cluster. Three of these objects are probably brown dwarfs, according to their spectral types (M8, M8.5, M8-L0). Three of the other new members may have edge-on disks, based on the shapes of their infrared spectral energy distributions. One of the possible edge-on systems has a steeply rising slope from 4.5 to 24um, indicating that it could be a Class I source (star+disk+envelope) rather than a Class II source (star+disk). If so, then it would be one of the least massive known Class I protostars (M5.75, M~0.1M_{sun}_).
- ID:
- ivo://CDS.VizieR/J/AJ/154/14
- Title:
- Low-mass stars in 25 Ori group and Orion OB1a
- Short Name:
- J/AJ/154/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Orion OB1a sub-association is a rich low-mass star (LMS) region. Previous spectroscopic studies have confirmed 160 LMSs in the 25 Orionis stellar group (25 Ori), which is the most prominent overdensity of Orion OB1a. Nonetheless, the current census of the 25 Ori members is estimated to be lower than 50% complete, leaving a large number of members to be still confirmed. We retrieved 172 low-resolution stellar spectra in Orion OB1a observed as ancillary science in the SDSS-III/BOSS survey, for which we classified their spectral types and determined physical parameters. To determine memberships, we analyzed the H{alpha} emission, LiI{lambda}6708 absorption, and NaI{lambda}{lambda}8183,8195 absorption as youth indicators in stars classified as M type. We report 50 new LMSs spread across the 25 Orionis, ASCC18, and ASCC20 stellar groups with spectral types from M0 to M6, corresponding to a mass range of 0.10{<=}m/M_{Sun}_{<=}0.58. This represents an increase of 50% in the number of known LMSs in the area and a net increase of 20% in the number of 25 Ori members in this mass range. Using parallax values from the Gaia DR1 catalog, we estimated the distances to these three stellar groups and found that they are all co-distant, at 338+/-66pc. We analyzed the spectral energy distributions of these LMSs and classified their disks into evolutionary classes. Using H-R diagrams, we found a suggestion that 25 Ori could be slightly older than the other two observed groups in Orion OB1a.
- ID:
- ivo://CDS.VizieR/J/A+A/488/167
- Title:
- Low-mass stars in {sigma} Ori and {lambda} Ori
- Short Name:
- J/A+A/488/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed a detailed membership selection and studied the accretion properties of low-mass stars in the two apparently very similar young (1-10Myr) clusters {sigma} Ori and {lambda} Ori. We observed 98 and 49 low-mass (0.2-1.0M_{sun}_stars in {sigma} Ori and {lambda} Ori respectively, using the multi-object optical spectrograph FLAMES at the VLT, with the high-resolution (R~17000) HR15N grating (6470-6790{AA}). We used radial velocities, Li and H{alpha} to establish cluster membership and H{alpha} and other optical emission lines to analyze the accretion properties of members. We identified 65 and 45 members of the {sigma} Ori and {lambda} Ori clusters, respectively, and discovered 16 new candidate binary systems.
- ID:
- ivo://CDS.VizieR/J/A+A/559/A3
- Title:
- Low-mass stars in Trumpler 37
- Short Name:
- J/A+A/559/A3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr 37. With a well-studied solar-type population, Tr 37 is a benchmark for disk evolution. We used low-resolution spectroscopy to identify and classify 141 members (78 new ones) and 64 probable members, mostly M-type stars. H{alpha} emission provides information about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the spectral energy distributions (SEDs) and search for disks. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, and dust-depleted disks.
- ID:
- ivo://CDS.VizieR/V/80
- Title:
- Low-Mass Stars' Membership in Alpha Persei Cluster
- Short Name:
- V/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog contains the tabulated results of a combined astrometric, photometric, and spectroscopic search for low-mass members in the intermediate-age open cluster Alpha Persei. It contains information on 132 new members and likely members, and 16 uncertain members of Alpha Per. The new membership information suggested to the author a revised age of the cluster to approximately 8x10+7yr. Tabulated data include AP number, VBI photometry, 1950 coordinates, relative proper motions with errors, H-alpha equivalent widths, and spectral type. Included are the individual membership determinations, based on H-alpha emission, spectral type, and echelle spectra data. The photometric data were obtained with the Lick Obs. 1-m Nickel Telescope using a TI 500x500 pixel CCD in B, V, and I bands. Low dispersion CCD spectra centered on H-alpha for candidates whose V-I photometry indicated likely membership using the Lick 1-m Nickel and 3-m Shane telescopes. High-dispersion echelle spectra were obtained for many bright candidates using the Hamilton echelle spectrographic with the Shane and Coude auxiliary telescopes.
