180 research outputs found
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
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
Welcome to the Twilight Zone: The Mid-Infrared Properties of Poststarburst Galaxies
We investigate the optical and Wide-field Survey Explorer (WISE) colors of
"E+A" identified post-starburst galaxies, including a deep analysis on 190
post-starbursts detected in the 2{\mu}m All Sky Survey Extended Source Catalog.
The post-starburst galaxies appear in both the optical green valley and the
WISE Infrared Transition Zone (IRTZ). Furthermore, we find that post-starbursts
occupy a distinct region [3.4]-[4.6] vs. [4.6]-[12] WISE colors, enabling the
identification of this class of transitioning galaxies through the use of
broad-band photometric criteria alone. We have investigated possible causes for
the WISE colors of post-starbursts by constructing a composite spectral energy
distribution (SED), finding that mid-infrared (4-12{\mu}m) properties of
post-starbursts are consistent with either 11.3{\mu}m polycyclic aromatic
hydrocarbon emission, or Thermally Pulsating Asymptotic Giant Branch (TP-AGB)
and post-AGB stars. The composite SED of extended post- starburst galaxies with
22{\mu}m emission detected with signal to noise >3 requires a hot dust
component to produce their observed rising mid-infrared SED between 12 and
22{\mu}m. The composite SED of WISE 22{\mu}m non-detections (S/N<3), created by
stacking 22{\mu}m images, is also flat, requiring a hot dust component. The
most likely source of this mid-infrared emission of these E+A galaxies is a
buried active galactic nucleus. The inferred upper limit to the Eddington
ratios of post-starbursts are 1e-2 to 1e-4, with an average of 1e-3. This
suggests that AGNs are not radiatively dominant in these systems. This could
mean that including selections able to identify active galactic nuclei as part
of a search for transitioning and post-starburst galaxies would create a more
complete census of the transition pathways taken as a galaxy quenches its star
formation.Comment: 13 pages, 11 figures, accepted for publication in the Astrophysical
Journa
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
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
SHOCKED POSTSTARBURST GALAXY SURVEY. II. the MOLECULAR GAS CONTENT and PROPERTIES of A SUBSET of SPOGs
We present CO(1–0) observations of objects within the Shocked POststarburst Galaxy Survey taken with the Institut de Radioastronomie Millimétrique 30 m single dish and the Combined Array for Research for Millimeter Astronomy interferometer. Shocked poststarburst galaxies (SPOGs) represent a transitioning population of galaxies, with deep Balmer absorption , consistent with an intermediate-age (A-star) stellar population, and ionized gas line ratios inconsistent with pure star formation. The CO(1–0) subsample was selected from SPOGs detected by the Wide-field Infrared Survey Explorer with 22 μm flux detected at a signal-to-noise ratio (S/N) > 3. Of the 52 objects observed in CO(1–0), 47 are detected with S/N > 3. A large fraction (37%–46% ± 7%) of our CO-SPOG sample were visually classified as morphologically disrupted. The H2 masses detected were between , consistent with the gas masses found in normal galaxies, though approximately an order of magnitude larger than the range seen in poststarburst galaxies. When comparing the 22 μm and CO(1–0) fluxes, SPOGs diverge from the normal star-forming relation, having 22 μm fluxes in excess of the relation by a factor of , suggestive of the presence of active galactic nuclei (AGNs). The Na i D characteristics of CO-SPOGs show that it is likely that many of these objects host interstellar winds. Objects with large Na i D enhancements also tend to emit in the radio, suggesting possible AGN driving of neutral winds
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