Mid-infrared Spectral Properties of Post-Starburst Quasars

We present Spitzer InfraRed Spectrograph (IRS) low-resolution spectra of 16 spectroscopically selected post-starburst quasars (PSQs) at z ~ 0.3. The optical spectra of these broad-lined active galactic nuclei (AGNs) simultaneously show spectral signatures of massive intermediate-aged stellar populations making them good candidates for studying the connections between AGNs and their hosts. The resulting spectra show relatively strong polycyclic aromatic hydrocarbon (PAH) emission features at 6.2 and 11.3\micron and a very weak silicate feature, indicative of ongoing star formation and low dust obscuration levels for the AGNs. We find that the mid-infrared composite spectrum of PSQs has spectral properties between ULIRGs and QSOs, suggesting that PSQs are hybrid AGN and starburst systems as also seen in their optical spectra. We also find that PSQs in early-type host galaxies tend to have relatively strong AGN activities, while those in spiral hosts have stronger PAH emission, indicating more star formation.Comment: 18 pages, 7 figures, 2 tables; Accepted for publication in ApJ: May 24, 201

Outflows and the Physical Properties of Quasars

We have investigated a sample of 5088 quasars from the Sloan Digital Sky Survey Second Data Release in order to determine how the frequency and properties of broad absorptions lines (BALs) depend on black hole mass, bolometric luminosity, Eddington fraction (L/L_Edd), and spectral slope. We focus only on high-ionization BALs and find a number of significant results. While quasars accreting near the Eddington limit are more likely to show BALs than lower $L/L_{Edd}$ systems, BALs are present in quasars accreting at only a few percent Eddington. We find a stronger effect with bolometric luminosity, such that the most luminous quasars are more likely to show BALs. There is an additional effect, previously known, that BAL quasars are redder on average than unabsorbed quasars. The strongest effects involving the quasar physical properties and BAL properties are related to terminal outflow velocity. Maximum observed outflow velocities increase with both the bolometric luminosity and the blueness of the spectral slope, suggesting that the ultraviolet luminosity to a great extent determines the acceleration. These results support the idea of outflow acceleration via ultraviolet line scattering.Comment: Uses emulateapj.cls, 14 pages including 7 tables and 7 figures. Accepted for publication in the Astrophysical Journal, Unabridged version of Table 4 can be downloaded from http://physics.uwyo.edu/agn

Shocked POststarbust Galaxy Survey I: Candidate Poststarbust Galaxies with Emission Line Ratios Consistent with Shocks

[Abridged] The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify transforming galaxies, in which the nebular lines are excited via shocks instead of through star formation processes. Utilizing the OSSY measurements on the Sloan Digital Sky Survey Data Release 7 catalog, we applied Balmer absorption and shock boundary criteria to identify 1,067 SPOG candidates (SPOGs*) within z=0.2. SPOGs* represent 0.2% of the OSSY sample galaxies that exceed the continuum signal-to-noise cut (and 0.7% of the emission line galaxy sample). SPOGs* colors suggest that they are in an earlier phase of transition than OSSY galaxies that meet an E+A selection. SPOGs* have a 13% 1.4GHz detection rate from the Faint Images of the Radio Sky at Twenty centimeters survey, higher than most other subsamples, and comparable only to low-ionization nuclear emission line region hosts, suggestive of the presence of active galactic nuclei. SPOGs* also have stronger NaD absorption than predicted from the stellar population, suggestive of cool gas being driven out in galactic winds. It appears that SPOGs* represent an earlier phase in galaxy transformation than traditionally selected poststarburst galaxies, and that a large proportion of SPOGs* also have properties consistent with disruption of their interstellar media, a key component to galaxy transformation. It is likely that many of the known pathways to transformation undergo a SPOG phase. Studying this sample of SPOGs* further, including their morphologies, active galactic nuclei properties, and environments, has the potential for us to build a more complete picture of the initial conditions that can lead to a galaxy evolving.Comment: 19 pages, 19 figures, 3 tables, accepted to ApJ Supplements (Apr 13), full sample is available on www.spogs.or

Catching Quenching Galaxies: The Nature of the WISE Infrared Transition Zone

We present the discovery of a prominent bifurcation between early-type galaxies and late-type galaxies, in [4.6]–[12] μm colors from the Wide Field Infrared Survey Explorer (WISE). We then use an emission-line diagnostic comparison sample to explore the nature of objects found both within and near the edges of this WISE infrared transition zone (IRTZ). We hypothesize that this bifurcation might be due to the presence of hot dust and polyaromatic hydrocarbon (PAH) emission features in late-type galaxies. Using a sample of galaxies selected through the Shocked Poststarburst Galaxy Survey (SPOGS), we are able to identify galaxies with strong Balmer absorption (EW(Hδ) > 5 Å) as well as emission lines inconsistent with star formation (deemed SPOG candidates, or SPOGs*) that lie within the optical green valley. Seyferts and low-ionization nuclear emission line regions, whose u − r colors tend to be red, are strongly represented within IRTZ, whereas SPOGs* tend to sit near the star-forming edge. Although active galactic nuclei are well represented in the IRTZ, we argue that the dominant IRTZ population is composed of galaxies that are in late stages of transitioning across the optical green valley, shedding the last of their remnant interstellar media

Black Hole - Bulge Relationship of Post-Starburst Quasars at z \sim 0.3

The MBH - {\sigma}\ast relation has been studied extensively for local galaxies, but to date there have been scarce few direct measurements of stellar velocity dispersions for systems beyond the local universe. We investigate black hole and host galaxy properties of six "post-starburst quasars" at z \sim 0.3. Spectra of these objects simultaneously display features from the active nucleus including broad emission lines and a host galaxy Balmer absorption series indicative of the post-starburst stellar population. These are the first measurements of {\sigma}\ast in such objects, and we significantly increase the number of directly-measured non-local objects on the MBH - {\sigma}\ast diagram. The "post-starburst quasars" of our sample fall on or above the locally defined MBH - {\sigma}\ast relation, a result that is consistent with previous MBH - {\sigma}\ast studies of samples at z > 0.1. However, they are generally consistent with the MBH-Lbulge relation. Futhermore, their location on the Faber-Jackson relation suggests that some of the bulges may be dynamically peculiar.Comment: 15 pages, 9 figures, accepted for publication in Ap

Now You See It, Now You Don't: The Disappearing Central Engine of the Quasar J1011+5442

We report the discovery of a new "changing-look" quasar, SDSS J101152.98+544206.4, through repeat spectroscopy from the Time Domain Spectroscopic Survey. This is an addition to a small but growing set of quasars whose blue continua and broad optical emission lines have been observed to decline by a large factor on a time scale of approximately a decade. The 5100 Angstrom monochromatic continuum luminosity of this quasar drops by a factor of > 9.8 in a rest-frame time interval of < 9.7 years, while the broad H-alpha luminosity drops by a factor of 55 in the same amount of time. The width of the broad H-alpha line increases in the dim state such that the black hole mass derived from the appropriate single-epoch scaling relation agrees between the two epochs within a factor of 3. The fluxes of the narrow emission lines do not appear to change between epochs. The light curve obtained by the Catalina Sky Survey suggests that the transition occurs within a rest-frame time interval of approximately 500 days. We examine three possible mechanisms for this transition suggested in the recent literature. An abrupt change in the reddening towards the central engine is disfavored by the substantial difference between the timescale to obscure the central engine and the observed timescale of the transition. A decaying tidal disruption flare is consistent with the decay rate of the light curve but not with the prolonged bright state preceding the decay, nor can this scenario provide the power required by the luminosities of the emission lines. An abrupt drop in the accretion rate onto the supermassive black hole appears to be the most plausible explanation for the rapid dimming.Comment: Submitted to MNRA

Towards an Understanding of Changing-Look Quasars: An Archival Spectroscopic Search in SDSS

The uncertain origin of the recently-discovered `changing-looking' quasar phenomenon -- in which a luminous quasar dims significantly to a quiescent state in repeat spectroscopy over ~10 year timescales -- may present unexpected challenges to our understanding of quasar accretion. To better understand this phenomenon, we take a first step to building a sample of changing-look quasars with a systematic but simple archival search for these objects in the Sloan Digital Sky Survey Data Release 12. By leveraging the >10 year baselines for objects with repeat spectroscopy, we uncover two new changing-look quasars, and a third discovered previously. Decomposition of the multi-epoch spectra and analysis of the broad emission lines suggest that the quasar accretion disk emission dims due to rapidly decreasing accretion rates (by factors of >2.5), while disfavoring changes in intrinsic dust extinction for the two objects where these analyses are possible. Broad emission line energetics also support intrinsic dimming of quasar emission as the origin for this phenomenon rather than transient tidal disruption events or supernovae. Although our search criteria included quasars at all redshifts and transitions from either quasar-like to galaxy-like states or the reverse, all of the clear cases of changing-look quasars discovered were at relatively low-redshift (z ~ 0.2 - 0.3) and only exhibit quasar-like to galaxy-like transitions.Comment: 15 pages, 8 figures. Updated to accepted versio

P-MaNGA : full spectral fitting and stellar population maps from prototype observations

MC acknowledges support from a Royal Society University Research Fellowship.MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a 6-yearSDSS-IV survey that will obtain resolved spectroscopy from 3600 Å to10300 Å for a representative sample of over 10,000 nearby galaxies.In this paper, we derive spatially resolved stellar population properties and radial gradients by performing full spectral fitting of observed galaxy spectra from P-MaNGA, a prototype of the MaNGA instrument. These data include spectra for eighteen galaxies, covering a large range of morphological type. We derive age, metallicity, dust and stellar mass maps, and their radial gradients, using high spectral-resolution stellar population models, and assess the impact of varying the stellar library input to the models. We introduce a method to determine dust extinction which is able to give smooth stellar mass maps even in cases of high and spatially non-uniform dust attenuation.With the spectral fitting we produce detailed maps of stellar population properties which allow us to identify galactic features among this diverse sample such as spiral structure, smooth radial profiles with little azimuthal structure in spheroidal galaxies, and spatially distinct galaxy sub-components. In agreement with the literature, we find the gradients for galaxies identified as early-type to be on average flat in age, and negative (- 0.15 dex / Re ) in metallicity,whereas the gradients for late-type galaxies are on average negative in age (- 0.39 dex / Re ) and flat in metallicity. We demonstrate howdifferent levels of data quality change the precision with which radialgradients can be measured. We show how this analysis, extended to thelarge numbers of MaNGA galaxies, will have the potential to shed lighton galaxy structure and evolution.PostprintPeer reviewe