Abstract
Weak emission-line quasars (WLQs) are a subset of type 1 quasars that exhibit extremely weak Ly
α
+ N
v
λ
1240 and/or C
iv
λ
1549 emission lines. We investigate the relationship between ...emission-line properties and accretion rate for a sample of 230 “ordinary” type 1 quasars and 18 WLQs at
z
< 0.5 and 1.5 <
z
< 3.5 that have rest-frame ultraviolet and optical spectral measurements. We apply a correction to the H
β
-based black hole mass (
M
BH
) estimates of these quasars using the strength of the optical Fe
ii
emission. We confirm previous findings that WLQs’
M
BH
values are overestimated by up to an order of magnitude using the traditional broad-emission-line region size–luminosity relation. With this
M
BH
correction, we find a significant correlation between H
β
-based Eddington luminosity ratios and a combination of the rest-frame C
iv
equivalent width and C
iv
blueshift with respect to the systemic redshift. This correlation holds for both ordinary quasars and WLQs, which suggests that the two-dimensional C
iv
parameter space can serve as an indicator of accretion rate in all type 1 quasars across a wide range of spectral properties.
ABSTRACT We release the next installment of the Stripe 82 X-ray survey point-source catalog, which currently covers 31.3 deg2 of the Sloan Digital Sky Survey (SDSS) Stripe 82 Legacy field. In total, ...6181 unique X-ray sources are significantly detected with XMM-Newton (>5 ) and Chandra (>4.5 ). This catalog release includes data from XMM-Newton cycle AO 13, which approximately doubled the Stripe 82X survey area. The flux limits of the Stripe 82X survey are 8.7 × 10−16 erg s−1 cm−2, 4.7 × 10−15 erg s−1 cm−2, and 2.1 × 10−15 erg s−1 cm−2 in the soft (0.5-2 keV), hard (2-10 keV), and full bands (0.5-10 keV), respectively, with approximate half-area survey flux limits of 5.4 × 10−15 erg s−1 cm−2, 2.9 × 10−14 erg s−1 cm−2, and 1.7 × 10−14 erg s−1 cm−2. We matched the X-ray source lists to available multi-wavelength catalogs, including updated matches to the previous release of the Stripe 82X survey; 88% of the sample is matched to a multi-wavelength counterpart. Due to the wide area of Stripe 82X and rich ancillary multi-wavelength data, including coadded SDSS photometry, mid-infrared WISE coverage, near-infrared coverage from UKIDSS and VISTA Hemisphere Survey, ultraviolet coverage from GALEX, radio coverage from FIRST, and far-infrared coverage from Herschel, as well as existing ∼30% optical spectroscopic completeness, we are beginning to uncover rare objects, such as obscured high-luminosity active galactic nuclei at high-redshift. The Stripe 82X point source catalog is a valuable data set for constraining how this population grows and evolves, as well as for studying how they interact with the galaxies in which they live.
Abstract
Quasars at
z
≳ 1 most often have redshifts measured from rest-frame ultraviolet emission lines. One of the most common such lines, C
iv
λ
1549, shows blueshifts up to ≈5000 km s
−1
and in ...rare cases even higher. This blueshifting results in highly uncertain redshifts when compared to redshift determinations from rest-frame optical emission lines, e.g., from the narrow O
iii
λ
5007 feature. We present spectroscopic measurements for 260 sources at 1.55 ≲
z
≲ 3.50 having −28.0 ≲
M
i
≲ − 30.0 mag from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS) catalog, augmenting the previous iteration, which contained 226 of the 260 sources whose measurements are improved upon in this work. We obtain reliable systemic redshifts based on O
iii
λ
5007 for a subset of 121 sources, which we use to calibrate prescriptions for correcting UV-based redshifts. These prescriptions are based on a regression analysis involving C
iv
full-width-at-half-maximum intensity and equivalent width, along with the UV continuum luminosity at a rest-frame wavelength of 1350 Å. Applying these corrections can improve the accuracy and the precision in the C
iv
-based redshift by up to ∼850 km s
−1
and ∼150 km s
−1
, respectively, which correspond to ∼8.5 and ∼1.5 Mpc in comoving distance at
z
= 2.5. Our prescriptions also improve the accuracy of the best available multifeature redshift determination algorithm by ∼100 km s
−1
, indicating that the spectroscopic properties of the C
iv
emission line can provide robust redshift estimates for high-redshift quasars. We discuss the prospects of our prescriptions for cosmological and quasar studies utilizing upcoming large spectroscopic surveys.
ABSTRACT In this work, we show how the stellar mass (M*) of galaxies affects the 3 < z < 4.6 Ly equivalent width (EW) distribution. To this end, we design a sample of 629 galaxies in the M* range ...from the 3D-HST/CANDELS survey. We perform spectroscopic observations of this sample using the Michigan/Magellan Fiber System, allowing us to measure Ly fluxes and use 3D-HST/CANDELS ancillary data. In order to study the Ly EW distribution dependence on M*, we split the whole sample in three stellar mass bins. We find that, in all bins, the distribution is best represented by an exponential profile of the form . Through a Bayesian analysis, we confirm that lower M* galaxies have higher Ly EWs. We also find that the fraction A of galaxies featuring emission and the e-folding scale W0 of the distribution anti-correlate with M*, recovering expressions of the forms and . These results are crucial for proper interpretation of Ly emission trends reported in the literature that may be affected by strong M* selection biases.
We present results of a ground-based near-infrared campaign with Palomar TripleSpec, Keck NIRSPEC, and Gemini GNIRS to target two samples of reddened active galactic nucleus (AGN) candidates from the ...31 deg2 Stripe 82 X-ray survey. One sample, which is ∼89% complete to (Vega), consists of eight confirmed AGNs, four of which were identified with our follow-up program, and is selected to have red R − K colors ( , Vega). The fainter sample ( , Vega) represents a pilot program to follow-up four sources from a parent sample of 34 that are not detected in the single-epoch SDSS catalog and have WISE quasar colors. All 12 sources are broad-line AGNs (at least one permitted emission line has an FWHM exceeding 1300 km s−1) and span a redshift range . Half the (R − K)-selected AGNs have features in their spectra suggestive of outflows. When comparing these sources to a matched sample of blue Type 1 AGNs, we find that the reddened AGNs are more distant ( ), and a greater percentage have high X-ray luminosities ( erg s−1). Such outflows and high luminosities may be consistent with the paradigm that reddened broad-line AGNs represent a transitory phase in AGN evolution as described by the major merger model for black hole growth. Results from our pilot program demonstrate proof of concept that our selection technique is successful in discovering reddened quasars at missed by optical surveys.
We analyse the stellar absorption features in high signal-to-noise ratio (S/N) near-infrared (NIR) spectra of the nuclear region of 12 nearby galaxies, mostly spirals. The features detected in some ...or all of the galaxies in this sample are the TiO (0.843 and 0.886 μm), VO (1.048 μm), CN (1.1 and 1.4 μm), H2O (1.4 and 1.9 μm) and CO (1.6 and 2.3 μm) bands. The C2 (1.17 and 1.76 μm) bands are generally weak or absent, although C2 (1.76 μm) may be weakly present in the mean galaxy spectrum. A deep feature near 0.93 μm, likely caused by CN, TiO and/or ZrO, is also detected in all objects. Fitting a combination of stellar spectra to the mean spectrum shows that the absorption features are produced by evolved stars: cool giants and supergiant stars in the early- or thermally pulsing asymptotic giant branch (E-AGB or TP-AGB) phases. The high luminosity of TP-AGB stars, and the appearance of VO and ZrO features in the data, suggest that TP-AGB stars dominate these spectral features. However, a contribution from other evolved stars is also likely. Comparison with evolutionary population synthesis models shows that models based on empirical libraries that predict relatively strong NIR features provide a more accurate description of the data. However, none of the models tested accurately reproduces all of the features observed in the spectra. To do so, the models will need to not only improve the treatment of TP-AGB stars, but also include good quality spectra of red giant and E-AGB stars. The uninterrupted wavelength coverage, high S/N and quantity of features we present here will provide a benchmark for the next generation of models aiming to explain and predict the NIR properties of galaxies.
We present near- and mid-IR observations of a sample of Seyfert II galaxies drawn from the 12 mu m Galaxy sample. The sample was observed in the J, H, K, L, M and N bands. Galaxy surface brightness ...profiles are modeled using nuclear, bulge, bar (when necessary), and disk components. To check the reliability of our findings, the procedure was tested using Spitzer observations of M 31. Nuclear spectral energy distributions (SEDs) are determined for 34 objects, and optical spectra are presented for 38, including analysis of their stellar populations using the STARLIGHT spectral synthesis code. Emission line diagnostic diagrams are used to discriminate between genuine active galactic nuclei (AGNs) and H II nuclei. Combining our observations with those found in the literature, we have a total of 40 SEDs. It is found that about 40% of the SEDs are characterized by an upturn in the near-IR, which we have quantified as a NIR slope alpha < 1 for an SED characterized as lambdafunctionof sub(lambda) is proportional to lambda super( alpha ). The three objects with an H II nucleus and two Seyfert nuclei with strong contamination from a circumnuclear also show an upturn. For genuine AGNs, this component could be explained as emission from the accretion disk, a jet, or from a very hot dust component leaking from the central region through a clumpy obscuring structure. The presence of a very compact nuclear starburst as the origin for this NIR excess emission is not favored by our spectroscopic data for these objects.
We present Gemini-North K-band spectra of two representative members of the class of high-redshift quasars with exceptionally weak rest-frame ultraviolet emission lines (WLQs), SDSS ...J114153.34+021924.3 at z = 3.55 and SDSS J123743.08+630144.9 at z = 3.49. In both sources, we detect an unusually weak broad H Delta *b line and place tight upper limits on the strengths of their O III lines. Virial, H Delta *b-based black hole mass determinations indicate normalized accretion rates of L/L Edd=0.4 for these sources, which is well within the range observed for typical quasars with similar luminosities and redshifts. We also present high-quality XMM-Newton imaging spectroscopy of SDSS J114153.34+021924.3 and find a hard-X-ray photon index of Delta *G = 1.91+0.24 --0.22, which supports the virial L/L Edd determination in this source. Our results suggest that the weakness of the broad emission lines in WLQs is not a consequence of an extreme continuum-emission source but instead due to abnormal broad emission line region properties.
We present Reverberation Mapping results after monitoring a sample of 17 high-z, high-luminosity quasars for more than 10 years using photometric and spectroscopic capabilities. Continuum and line ...emission flux variability is observed in all quasars. Using cross-correlation analysis we successfully determine lags between the variations in the continuum and broad emission lines for several sources. Here we present a highlight of our results and the determined radius–luminosity relations for Lyα and CIV.
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