171 research outputs found
Superluminous Spiral Galaxies
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster galaxies, with r-band monochromatic luminosity L_r = 8–14L* (4.3–7.5 × 10^(44) erg s^(−1)). These super spiral galaxies are also giant and massive, with diameter D = 57–134 kpc and stellar mass M_(stars) = 0.3–3.4 × 10^(11)M⊙. We find 53 super spirals out of a complete sample of 1616 SDSS galaxies with redshift z 8L*. The closest example is found at z = 0.089. We use existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS and Wide-field Infrared Survey Explorer colors are consistent with normal star-forming spirals on the blue sequence. However, the extreme masses and rapid SFRs of 5–65 M⊙ yr^(−1) place super spirals in a sparsely populated region of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a diverse range of environments, from isolation to cluster centers. We find four super spiral galaxy systems that are late-stage major mergers—a possible clue to their formation. We suggest that super spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become massive lenticular galaxies after they are cut off from their gas supply and their disks fade
A Catalog of the Most Optically Luminous Galaxies at z < 0.3: Super Spirals, Super Lenticulars, Super Post-Mergers, and Giant Ellipticals
We present a catalog of the 1525 most optically luminous galaxies from the Sloan Digital Sky Survey with r-band luminosity L_r > 8L* and redshift z < 0.3, including 84 super spirals, 15 super lenticulars, 14 super post-merger galaxies, and 1400 giant ellipticals. With mass in stars of 10^(11.3)–10^(12) M⊙, super spirals and lenticulars are the most massive disk galaxies currently known. The specific star formation rates of super spirals place them on or below the star-forming main sequence. They must have formed stars at a high rate throughout their history in order to grow their massive, gigantic stellar disks and maintain their blue u − r integrated colors. Their disks are red on the inside and blue on the outside, consistent with inside-out growth. They tend to have small bulge-to-total (B/T) r-band luminosity ratios, characteristic of disk building via minor mergers and cold accretion. A large percentage of super disk galaxies (41%) have double nuclei, double disks, or other signatures of ongoing mergers. Most (72%) are found in moderate- to low-density environments, while the rest are found at the outskirts of clusters. It is likely that super spirals survive in these environments because they continue to accrete cold gas and experience only minor mergers at late times, by virtue of their enormous masses and angular momenta. We suggest that super post-mergers are the product of super spiral major mergers and may be the precursors of some giant elliptical galaxies found in low-density environments. We present two new gravitational lens candidates in an appendix
Structure of the Accretion Flow in Broad-Line Radio Galaxies: The Case of 3C390.3
We present XMM and Suzaku observations of the Broad-Line Radio Galaxy (BLRG)
3C390.3. The Fe Ka line has a width FWHM ~ 8,800 km/s, consistent within a
factor two with the width of the double-peaked H_alpha line, suggesting an
origin from the Broad Line Region. The data show for the first time a weak,
broad bump extending from 5 to 7 keV. When fitted with a Gaussian, its centroid
energy is 6.6 keV in the source's rest-frame with FWHM of 43,000 km/s and EW of
50 eV; its most likely interpretation is emission from He-like Fe (Fe XXV),
suggesting the presence of an ionized medium in the inner regions of 3C390.3.
The broad-band 0.5-100 keV continuum is well described by a single power law
with photon index Gamma=1.6 and cutoff energy 157 keV, plus cold reflection
with strength R=0.5. In addition, ionized reflection is required to account for
the 6.6 keV bump in the broad-band continuum, yielding an ionization parameter
xi ~ 2700 ergs cm s^-1; the inner radius of the ionized reflector is
constrained to be larger than 20 r_G, although this result depends on the
assumed emissivity profile of the disk. If true, we argue that the lack of
broad Fe K emission from within 20 r_G indicates that the innermost regions of
the disk in 3C390.3 are obscured and/or poorly illuminated. While the SED of
3C390.3 is generally dominated by accretion-related continuum, during accretion
low states the jet can significantly contribute in the optical to X-ray bands
via synchrotron self-Compton emission. (Abridged)Comment: 7 figures, 5 tables, accepted for publication in Ap
Suzaku Observations of Iron Lines and Reflection in AGN
Initial results on the iron K-shell line and reflection component in several
AGN observed as part of the Suzaku Guaranteed time program are reviewed. This
paper discusses a small sample of Compton-thin Seyferts observed to date with
Suzaku; namely MCG -5-23-16, MCG -6-30-15, NGC 4051, NGC 3516, NGC 2110, 3C 120
and NGC 2992. The broad iron K emission line appears to be present in
all but one of these Seyfert galaxies, while the narrow core of the line from
distant matter is ubiquitous in all the observations. The iron line in MCG
-6-30-15 shows the most extreme relativistic blurring of all the objects, the
red-wing of the line requires the inner accretion disk to extend inwards to
within 2.2Rg of the black hole, in agreement with the XMM-Newton observations.
Strong excess emission in the Hard X-ray Detector (HXD) above 10 keV is
observed in many of these Seyfert galaxies, consistent with the presence of a
reflection component from reprocessing in Compton-thick matter (e.g. the
accretion disk). Only one Seyfert galaxy (NGC 2110) shows neither a broad iron
line nor a reflection component. The spectral variability of MCG -6-30-15, MCG
-5-23-16 and NGC 4051 is also discussed. In all 3 cases, the spectra appear
harder when the source is fainter, while there is little variability of the
iron line or reflection component with source flux. This agrees with a simple
two component spectral model, whereby the variable emission is the primary
power-law, while the iron line and reflection component remain relatively
constant.Comment: 8 pages. Accepted for publication in Astronomical Notes (proceedings
of invited talk given at "Variable and Broad Iron lines around Black Holes",
ESAC, Madrid, Spain, 26-28 June 2006
XMM-Newton View of the Multi-Phase Warm Absorber in Seyfert 1 Galaxy NGC985
We present an analysis of an XMM-Newton observation of the Seyfert 1 Galaxy
NGC 985. The EPIC spectra present strong residuals to a single power-law model,
indicating the presence of ionized absorbing gas and a soft excess. A
broad-band fit to the EPIC and RGS spectra shows that the continuum can be well
fit with a power-law and a blackbody component. The RGS can be modeled either
with two or three absorption components. In the two absorber model the
low-ionization one, accounts for the presence of the Fe M-shell unresolved
transition array (Fe VII-XIII), and the high ionization component is required
by the presence of several Fe L-shell transitions. The data suggest the
presence of a third ionized component with higher ionization, so that the Fe
L-shell absorption features are produced by two different components (one
producing absorption by Fe XVII-XX, and the other absorption by Fe XX-XXII).
However, the presence of the third absorbing component cannot be detected by
means of an isolated absorption line in a significant way, so we consider this
detection only as tentative. Interestingly, all ionization components have
similar kinematics. In addition, whether two or three absorbers are considered,
the components appear to be in pressure balance. These results give further
support to the idea that warm absorbers in AGN consist of a two or three-phase
medium. We note that, while in the model with only two absorbers one of them
(the high ionization component) lies on an unstable branch of the thermal
equilibrium curve, in the model with three absorbers all of the components lie
on stable branches of the curve. This gives further plausibility to a
multi-phase absorber.Comment: Acepted for publication in Ap
Warm H as a probe of massive accretion and feedback through shocks and turbulence across cosmic time
Galaxy formation depends on a complex interplay between gravitational
collapse, gas accretion, merging, and feedback processes. Yet, after many
decades of investigation, these concepts are poorly understood. This paper
presents the argument that warm H can be used as a tool to unlock some of
these mysteries. Turbulence, shocks and outflows, driven by star formation, AGN
activity or inflows, may prevent the rapid buildup of star formation in
galaxies. Central to our understanding of how gas is converted into stars is
the process by which gas can dissipate its mechanical energy through turbulence
and shocks in order to cool. H lines provide direct quantitative
measurements of kinetic energy dissipation in molecular gas in galaxies
throughout the Universe. Based on the detection of very powerful H lines
from z = 2 galaxies and proto-clusters at the detection limits of {\it
Spitzer}, we are confident that future far-IR and UV H observations will
provide a wealth of new information and insight into galaxy evolution to
high-z. Finally, at the very earliest epoch of star and galaxy formation, warm
H may also provide a unique glimpse of molecular gas collapse at 7 z
12 in massive dark matter (DM) halos on their way to forming the very first
galaxies. Such measurements are beyond the reach of existing and planned
observatories.Comment: Submitted as a science White Paper to the Astronomy and Astrophysics
Astro 2020 Decadal Survey call issued by the National Academies of Sciences,
Engineering and Medicine (March 11 2019
Aromatic Features in AGN: Star-Forming Infrared Luminosity Function of AGN Host Galaxies
We describe observations of aromatic features at 7.7 and 11.3 um in AGN of
three types including PG, 2MASS and 3CR objects. The feature has been
demonstrated to originate predominantly from star formation. Based on the
aromatic-derived star forming luminosity, we find that the far-IR emission of
AGN can be dominated by either star formation or nuclear emission; the average
contribution from star formation is around 25% at 70 and 160 um. The
star-forming infrared luminosity functions of the three types of AGN are
flatter than that of field galaxies, implying nuclear activity and star
formation tend to be enhanced together. The star-forming luminosity function is
also a function of the strength of nuclear activity from normal galaxies to the
bright quasars, with luminosity functions becoming flatter for more intense
nuclear activity. Different types of AGN show different distributions in the
level of star formation activity, with 2MASS> PG> 3CR star formation rates.Comment: Accepted for publication in ApJ, 24 pages, 13 figure
Cosmic Evolution of Star Formation In SDSS Quasar Hosts Since z=1
We present Spitzer IRS observations of a complete sample of 57 SDSS type-1
quasars at z~1. Aromatic features at 6.2 and/or 7.7 um are detected in about
half of the sample and show profiles similar to those seen in normal galaxies
at both low- and high-redshift, indicating a star-formation origin for the
features. Based on the ratio of aromatic to star-formation IR (SFIR)
luminosities for normal star-forming galaxies at z~1, we have constructed the
SFIR luminosity function (LF) of z~1 quasars. As we found earlier for
low-redshift PG quasars, these z~1 quasars show a flatter SFIR LF than do z~1
field galaxies, implying the quasar host galaxy population has on average a
higher SFR than the field galaxies do. As measured from their SFIR LF,
individual quasar hosts have on average LIRG-level SFRs, which mainly arise in
the circumnuclear regions. By comparing with similar measurements of
low-redshift PG quasars, we find that the comoving SFIR luminosity density in
quasar hosts shows a much larger increase with redshift than that in field
galaxies. The behavior is consistent with pure density evolution since the
average SFR and the average SFR/BH-accretion-rate in quasar hosts show little
evolution with redshift. For individual quasars, we have found a correlation
between the aromatic-based SFR and the luminosity of the nuclear radiation,
consistent with predictions of some theoretical models. We propose that type 1
quasars reside in a distinct galaxy population that shows elliptical morphology
but that harbors a significant fraction of intermediate-age stars and is
experiencing intense circumnuclear star formation.Comment: Accepted for publication in ApJ, 20 pages, 11 figure
- …