Host Galaxies and the Spectral Variability of Quasars

Astronomy & Astrophysics, 2011

Context. Mass-loss from evolved stars chemically enriches the interstellar medium (ISM). Stellar winds from massive stars and their explosions as supernovae shape the ISM and trigger star formation. Studying evolved stars is fundamental for understanding galaxy formation and evolution at any redshift. Aims. We aim to establish a photometric classification scheme for Galactic mass-losing evolved stars (e.g., WR, RSG, and AGB stars) with the goal of identifying new ones, and subsequently to use these samples as tracers of Galactic structure. Methods. We searched for counterparts of known Galactic WR, LBV, RSG, and O-rich AGB stars in the 2MASS, GLIMPSE, and MSX catalogs, and we analyzed their properties with near-and mid-infrared color-color diagrams. Results. We used the Q1 parameter, which is a measure of the deviation from the interstellar reddening vector in the J − H versus H−K s diagram, and we defined a new parameter, Q2, which is a measure of the deviation from the interstellar reddening vector in the J−K s versus K s-[8.0] diagram. The latter plane enables to distinguish between interstellar and circumstellar reddening, and to identify stars with circumstellar envelopes. WR stars and late-type mass-losing stars (AGBs and RSGs) are distributed in two different regions of the Q1 versus K s-[8.0] diagram. A sequence of increasing [3.6]-[4.5] and [3.6]-[8.0] colors with increasing pulsation amplitudes (SRs, Miras, and OH/IR stars) is found. Spectra of Miras and OH/IR stars have stronger water absorption at 3.0 μm than SR stars or most of the RSGs. Masing Miras stars have water, but stronger SiO (∼4 μm) and CO 2 absorption (∼4.25 μm), as suggested by their [3.6]-[4.5] colors, bluer than those of non masing stars. A fraction of RSGs (22%) have the bluest [3.6]-[4.5] colors, but small Q2 values. We propose a new set of photometric criteria to distinguish among IR bright Galactic stars. Conclusions. The GLIMPSE catalog is a powerful tool for photometric classification of Galactic mass-losing evolved stars. Our new criteria will yield many new RSGs and WRs.

Monthly Notices of the Royal Astronomical Society, 2010

There is increasing evidence of a connection between AGN activity and galaxy evolution. To obtain further insight into this potentially important evolutionary phase, we analyse the properties of quasar host galaxies. In this paper, we present a population synthesis modeling technique for off-axis spectra, the results of which constrain host colour and the stellar ages of luminous quasars (M V (nuc) < −23). Our technique is similar to well established quiescent-galaxy models, modified to accommodate scattered nuclear light (a combination of atmospheric, instrumental and host galaxy scattered light) observed off axis. In our model, subtraction of residual scattered quasar light is performed, while simultaneously modeling the constituent stellar populations of the host galaxy. The reliability of this technique is tested via a Monte-Carlo routine in which the correspondence between synthetic spectra with known parameters and the model output is determined. Application of this model to a preliminary sample of 10 objects is presented and compared to previous studies. Spectroscopic data was obtained via long-slit and integral-field unit observations on the Keck and WIYN telescopes. We confirm that elliptical quasar hosts are distinguishable (bluer) from inactive ellipticals in rest frame B-V colour. Additionally, we note a trend for radio luminous (L 5GHz 10 40 erg s −1 ) quasars to be located in redder host galaxies in comparison to their less luminous radio counterparts. While the host colour and age of our radio luminous sample is in close proximity to the green valley, our radio faint sample is consistent with quiescent star-forming galaxies. However, further observations are needed to confirm these results. Finally, we discuss future applications for our technique on a larger sample of objects being obtained via SALT and WIYN telescope observing campaigns.

Astronomy & Astrophysics, 2013

Quasi-stellar objects (QSOs) occur in galaxies where supermassive black holes (SMBHs) are growing substantially through rapid accretion of gas. Many popular models of the co-evolutionary growth of galaxies and black holes predict that QSOs are also sites of substantial recent star formation (SF), mediated by important processes, such as major mergers, which rapidly transform the nature of galaxies. A detailed study of the star-forming properties of QSOs is a critical test of such models. We present a far-infrared Herschel/PACS study of the mean star formation rate (SFR) of a sample of spectroscopically observed QSOs to z ∼ 2 from the COSMOS extragalactic survey. This is the largest sample to date of moderately luminous QSOs (AGN luminosities that lie around the knee of the luminosity function) studied using uniform, deep far-infrared photometry. We study trends of the mean SFR with redshift, black hole mass, nuclear bolometric luminosity and specific accretion rate (Eddington ratio). To minimize systematics, we have undertaken a uniform determination of SMBH properties, as well as an analysis of important selection effects of spectroscopic QSO samples that influence the interpretation of SFR trends. We find that the mean SFRs of these QSOs are consistent with those of normal massive star-forming galaxies with a fixed scaling between SMBH and galaxy mass at all redshifts. No strong enhancement in SFR is found even among the most rapidly accreting systems, at odds with several co-evolutionary models. Finally, we consider the qualitative effects on mean SFR trends from different assumptions about the SF properties of QSO hosts and from redshift evolution of the SMBH-galaxy relationship. While limited currently by uncertainties, valuable constraints on AGN-galaxy co-evolution can emerge from our approach.

1993

This thesis describes an infrared search for the intervening galaxies responsible for some of the heavy-element absorption lines observed in QSO spectra. Deep K-band images have been obtained of 11 QSOs whose spectra are known to contain multiple CIV absorption systems in the redshift range 1.2 ˂ z ˂ 2.0. After background subtraction, a clear excess of sources is detected within a small angular separation (≈ 6.&quot;0) of the QSOs. We discuss the possible origins of this excess, in particular the hypotheses that the excess arises from QSO-galaxy associations or from MgII systems at lower redshifts, but consider them unlikely in the light of previous studies. We thus conclude that the excess objects are most likely to be associated with the CIV absorption systems. Prom a final sample of 19 candidate absorbers with a mean redshift 1 - 1.6, we find that the absorbing candidate population consists of bright L* galaxies whose luminosities are similar to their present-day counterparts. Th...

The Astronomical …, 2001

We present an empirical investigation of the colors of quasars in the Sloan Digital Sky Survey (SDSS) photometric system. The sample studied includes 2625 quasars with SDSS photometry : 1759 quasars found during SDSS spectroscopic commissioning and SDSS follow-up observations on other telescopes, 50 matches to FIRST quasars, 573 matches to quasars from the NASA Extragalactic Database, and 243 quasars from two or more of these sources. The quasars are distributed in a wide stripe centered on 2¡ .5 the celestial equator covering D529 deg2. Positions (accurate to and SDSS magnitudes are given for 0A .2) the 898 quasars known prior to SDSS spectroscopic commissioning. New SDSS quasars, which range in brightness from i* \ 15.39 to the photometric magnitude limit of the survey, represent an increase of over 200% in the number of known quasars in this area of the sky. The ensemble average of the observed colors of quasars in the SDSS passbands are well represented by a power-law continuum with and are close to those predicted by previous simulations. However, the contributions a l \ [0.5 ( f l P la) of the "" small blue (or j3000) bump ÏÏ and other strong emission lines have a signiÐcant e †ect upon the colors. The color-redshift relation exhibits considerable structure, which may be of use in determining photometric redshifts for quasars from their colors alone. The range of colors at a given redshift can generally be accounted for by a range in the optical spectral index with a distribution a l \ [0.5^0.65 ÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈ 2308 COLORS OF 2625 QUASARS 2309 (95% conÐdence), but there is a red tail in the distribution. This tail may be a sign of internal reddening, especially since fainter objects at a given redshift tend to exhibit redder colors than the average. Finally, we show that there is a continuum of properties between quasars and Seyfert galaxies, and we test the validity of the traditional dividing line between the two classes of active galactic nuclei. (M B \ [23)

Monthly Notices of the Royal Astronomical Society, 1999

March and 1996 July. A distinctive feature of this survey is its photometric accuracy, , 0X02 V magY achieved through differential photometry with CCD detectors, which allows the detection of faint levels of variability. We find that the relative variability, d saL, observed in the V band is anticorrelated with both luminosity and redshift, although we have no means of discovering the dominant relation, given the strong coupling between luminosity and redshift for the objects in our sample. We introduce a model for the dependence of quasar variability on frequency that is consistent with multiwavelength observations of the nuclear variability of the Seyfert galaxy NGC 4151. We show that correcting the observed variability for this effect slightly increases the significance of the trends of variability with luminosity and redshift. Assuming that variability depends only on the luminosity, we show that the corrected variability is anticorrelated with luminosity and is in good agreement with predictions of a simple Poissonian model. The energy derived for the hypothetical pulses, , 10 50 erg, agrees well with those obtained in other studies. We also find that the radio-loud objects in our sample tend to be more variable than the radio-quiet ones, for all luminosities and redshifts.

2016

We have improved upon our previous search technique of systematically searching QSO spectra for narrow galactic Hα emission, which indicates a foreground galaxy within the Sloan Digital Sky Survey (SDSS) spectral fiber. We now search for Hα plus eight other galactic emission lines in the same manner. We have scanned the SDSS DR7 QSO catalog spectra searching for these emission lines. Here we present our sample which focuses on the redshift range z &lt; 0.401 where galactic Hα is detectable in the SDSS spectra. This has revealed 27 unique galaxies on top of QSOs (GOTOQs). We have deblended the QSOs from the respective galaxies and determined the photometric properties of these systems. We find upon deblending that most of the galaxies are

Arxiv preprint astro-ph/ …, 2006

We report on the relative optical variability of the three brightest nearby quasars, 3C 273, PDS 456, and PHL 1811. All three have comparable absolute magnitudes, but PDS 456 and PHL 1811 are radio quiet. PDS 456 is a broadline object, but PHL 1811 could be classified as a high-luminosity Narrow-Line Seyfert 1 (NLS1). Both of the radio-quiet quasars show significant variability on a timescale of a few days. The seasonal rms V-band variability amplitudes of 3C 273 and PDS 456 are indistinguishable, and the seasonal rms variability amplitude of PHL 1811 was only exceeded by 3C 273 once in 30 years of monitoring. We find no evidence that the optical variability of 3C 273 is greater than or more rapid than the variability of the comparably-bright, radio-quiet quasars. This suggests that not only do radio-loud and radio-quiet AGNs have similar spectral energy distributions, but that the variability mechanisms are also similar. The optical variability of 3C 273 is not dominated by a "blazar" component.

The Astrophysical Journal, 1999

We have obtained H-band spectra of 32 luminous quasars at 2.0 ¹ z ¹ 2.5 with the Multiple Mirror Telescope. The sample contains 15 radio-loud quasars (RLQs) and 17 radio-quiet quasars (RQQs). We have measured emission line properties from the rest-frame wavelength range of approximately jj4500È 5500 by Ðtting the data with composite model spectra. Our analysis includes comparison of RLQs versus RQQs, as well as comparison between the broad-absorption-line quasar (BALQSO) and nonÈbroadabsorption-line quasar (nonBALQSO) subsets of the RQQ sample. In addition, we calculated the complete correlation matrix of the measured properties. We combined our high-redshift sample with the sample of 87 low-redshift quasars from Boroson & Green to determine the luminosity and redshift dependences of the measured emission properties.

Astronomy & Astrophysics, 2003

We present the first statistical analysis of the complete ESO-Sculptor Survey (ESS) of faint galaxies. The fluxcalibrated sample of 617 galaxies with R c ≤ 20.5 is separated into 3 spectral classes, based on a principal component analysis which provides a continuous and template-independent spectral classification. We use an original method to estimate accurate K-corrections: comparison of the ESS spectra with a spectral library using the principal component analysis allows us to extrapolate the missing parts of the observed spectra at blue wavelengths, then providing a polynomial parameterization of K-corrections as a function of spectral type and redshift. We also report on all sources of random and systematic errors which affect the spectral classification, the K-corrections, and the resulting absolute magnitudes. We use the absolute magnitudes to measure the Johnson-Cousins B, V, R c luminosity functions of the ESS as a function of spectral class. The shape of the derived luminosity functions show marked differences among the 3 spectral classes, which are common to the B, V, R c bands, and therefore reflect a physical phenomenon: for galaxies of later spectral type, the characteristic magnitude is fainter and the faint-end is steeper. The ESS also provides the first estimates of luminosity functions per spectral type in the V band. The salient results are obtained by fitting the ESS luminosity functions with composite functions based on the intrinsic luminosity functions per morphological type measured locally by Sandage et al. (1985) and Jerjen & Tammann (1997). The Gaussian luminosity functions for the nearby Spiral galaxies can be reconciled with the ESS intermediate and late-type luminosity functions if the corresponding classes contain an additional Schechter contribution from Spheroidal and Irregular dwarf galaxies, respectively. The present analysis of the ESS luminosity functions offers a renewed interpretation of the galaxy luminosity function from redshift surveys. It also illustrates how luminosity functions per spectral type may be affected by morphological type mixing, and emphasizes the need for a quantitative morphological classification at z > ∼ 0.1 which separates the giant and dwarf galaxy populations.