21 research outputs found
Star Formation in QSO Host Galaxies
Many of the conditions that are necessary for starbursts appear to be
important in the triggering of QSOs. However, it is still debatable whether
starbursts are ubiquitously present in galaxies harboring QSOs. In this paper
we review our current knowledge from observations of the role of starbursts in
different types of QSOs. Post-starburst stellar populations are potentially
present in the majority of QSO hosts. QSOs with far-infrared colors similar to
those of ultraluminous infrared galaxies invariably reside in merging galaxies
that have interaction-induced starbursts of a few hundred Myr or less. Similar,
but dramatically more luminous post-starburst populations are found in the
recently discovered class of QSOs known as post-starburst QSOs, or Q+A's. Both
of these classes, however, comprise only a small fraction (10-15%) of the total
QSO population. The so-called "red" QSOs generally suffer from strong
extinction at optical wavelengths, making them ideal candidates for the study
of hosts. Their stellar populations typically show a post-starburst component
as well, though with a larger range of ages. Finally, optical "classical" QSO
hosts show traces of major star formation episodes (typically involving >10% of
the mass of the stellar component) in the more distant past (1-2 Gyr). These
starbursts appear to be linked to past merger events. It remains to be
determined whether these mergers were also responsible for triggering the QSO
activity that we observe today.Comment: 8 pages, 5 figures, invited review for "QSO Host Galaxies: Evolution
and Environment", held at the Lorentz Center, Universiteit Leiden, August,
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The Spitzer Local Volume Legacy: Survey Description and Infrared Photometry
The survey description and the near-, mid-, and far-infrared flux properties
are presented for the 258 galaxies in the Local Volume Legacy (LVL). LVL is a
Spitzer Space Telescope legacy program that surveys the local universe out to
11 Mpc, built upon a foundation of ultraviolet, H-alpha, and HST imaging from
11HUGS (11 Mpc H-alpha and Ultraviolet Galaxy Survey) and ANGST (ACS Nearby
Galaxy Survey Treasury). LVL covers an unbiased, representative, and
statistically robust sample of nearby star-forming galaxies, exploiting the
highest extragalactic spatial resolution achievable with Spitzer. As a result
of its approximately volume-limited nature, LVL augments previous Spitzer
observations of present-day galaxies with improved sampling of the
low-luminosity galaxy population. The collection of LVL galaxies shows a large
spread in mid-infrared colors, likely due to the conspicuous deficiency of 8um
PAH emission from low-metallicity, low-luminosity galaxies. Conversely, the
far-infrared emission tightly tracks the total infrared emission, with a
dispersion in their flux ratio of only 0.1 dex. In terms of the relation
between infrared-to-ultraviolet ratio and ultraviolet spectral slope, the LVL
sample shows redder colors and/or lower infrared-to-ultraviolet ratios than
starburst galaxies, suggesting that reprocessing by dust is less important in
the lower mass systems that dominate the LVL sample. Comparisons with
theoretical models suggest that the amplitude of deviations from the relation
found for starburst galaxies correlates with the age of the stellar populations
that dominate the ultraviolet/optical luminosities.Comment: Accepted for publication in ApJ; Figures 1,8,9 provided as jpeg
The Calibration of Monochromatic Far-Infrared Star Formation Rate Indicators
(Abridged) Spitzer data at 24, 70, and 160 micron and ground-based H-alpha
images are analyzed for a sample of 189 nearby star-forming and starburst
galaxies to investigate whether reliable star formation rate (SFR) indicators
can be defined using the monochromatic infrared dust emission centered at 70
and 160 micron. We compare recently published recipes for SFR measures using
combinations of the 24 micron and observed H-alpha luminosities with those
using 24 micron luminosity alone. From these comparisons, we derive a reference
SFR indicator for use in our analysis. Linear correlations between SFR and the
70 and 160 micron luminosity are found for L(70)>=1.4x10^{42} erg/s and
L(160)>=2x10^{42} erg/s, corresponding to SFR>=0.1-0.3 M_sun/yr. Below those
two luminosity limits, the relation between SFR and 70 micron (160 micron)
luminosity is non-linear and SFR calibrations become problematic. The
dispersion of the data around the mean trend increases for increasing
wavelength, becoming about 25% (factor ~2) larger at 70 (160) micron than at 24
micron. The increasing dispersion is likely an effect of the increasing
contribution to the infrared emission of dust heated by stellar populations not
associated with the current star formation. The non-linear relation between SFR
and the 70 and 160 micron emission at faint galaxy luminosities suggests that
the increasing transparency of the interstellar medium, decreasing effective
dust temperature, and decreasing filling factor of star forming regions across
the galaxy become important factors for decreasing luminosity. The SFR
calibrations are provided for galaxies with oxygen abundance 12+Log(O/H)>8.1.
At lower metallicity the infrared luminosity no longer reliably traces the SFR
because galaxies are less dusty and more transparent.Comment: 69 pages, 19 figures, 2 tables; accepted for publication on Ap
Are red 2MASS QSOs young?
We use photometric data from Spitzer to explore the mid- and far-IR
properties of 10 red QSOs (J-K>2, R-K>5) selected by combining the 2MASS in the
NIR with the SDSS at optical wavelengths. Optical and/or near-infrared spectra
are available for 8/10 sources. Modeling the SED from UV to far-IR shows that
moderate dust reddening (A_V=1.3-3.2) can explain the red optical and near-IR
colours of the sources in the sample. There is also evidence that red QSOs have
60/12micron luminosity ratio higher than PG QSOs (97% significance). This can
be interpreted as a higher level of star-formation in these systems (measured
by the 60micron luminosity) for a given AGN power (approximated by the 12micron
luminosity). This is consistent with a picture where red QSOs represent an
early phase of AGN evolution, when the supermassive black hole is enshrouded in
dust and gas clouds, which will eventually be blown out (possibly by AGN driven
outflows) and the system will appear as typical optically luminous QSO. There
is also tentative evidence significant at the 96% level that red 2MASS QSOs are
more often associated with radio emission than optically selected SDSS QSOs.
This may indicate outflows, also consistent with the young AGN interpretation.
We also estimate the space density of red QSOs relative to optically selected
SDSS QSOs, taking into account the effect of dust extinction and the intrinsic
luminosity of the sources. We estimate that the fraction of red QSOs in the
overall population increases from 3% at M_K=-27.5mag to 12% at M_K=-29.5mag.
This suggests that reddened QSOs become more important at the bright end of the
Luminosity Function. If red QSOs are transition objects on the way to becoming
typical optically luminous QSOs, the low fractions above suggest that these
systems spent <12% of their lifetime at the "reddened" stage.Comment: Accepted by MNRA
The British Army, information management and the First World War revolution in military affairs
Information Management (IM) â the systematic ordering, processing and channelling of information within organisations â forms a critical component of modern military command and control systems. As a subject of scholarly enquiry, however, the history of military IM has been relatively poorly served. Employing new
and under-utilised archival sources, this article takes the British Expeditionary Force (BEF) of the First World War as its case study and assesses the extent to which its IM system contributed to the emergence of the modern battlefield in 1918. It argues that the
demands of fighting a modern war resulted in a general, but not universal, improvement in the BEFâs IM techniques, which in turn laid the groundwork, albeit in embryonic form, for the IM systems of modern armies.
KEY WORDS: British Army, Information Management, First World War, Revolution in Military Affairs, Adaptatio
Host-Galaxy Properties of 32 Low-Redshift Superluminous Supernovae from the Palomar Transient Factory
The American Astronomical Society. All rights reserved..We present ultraviolet through near-infrared photometry and spectroscopy of the host galaxies of all superluminous supernovae (SLSNe) discovered by the Palomar Transient Factory prior to 2013 and derive measurements of their luminosities, star formation rates, stellar masses, and gas-phase metallicities. We find that Type I (hydrogen-poor) SLSNe (SLSNe I) are found almost exclusively in low-mass (Mâ >2x109 Mâ) and metal-poor (12+log10[O/H] <8.4) galaxies. We compare the mass and metallicity distributions of our sample to nearby galaxy catalogs in detail and conclude that the rate of SLSNe I as a fraction of all SNe is heavily suppressed in galaxies with metallicities âł0.5 Zâ. Extremely low metallicities are not required and indeed provide no further increase in the relative SLSN rate. Several SLSN I hosts are undergoing vigorous starbursts, but this may simply be a side effect of metallicity dependence: dwarf galaxies tend to have bursty star formation histories. Type II (hydrogen-rich) SLSNe (SLSNe II) are found over the entire range of galaxy masses and metallicities, and their integrated properties do not suggest a strong preference for (or against) low-mass/low-metallicity galaxies. Two hosts exhibit unusual properties: PTF 10uhf is an SLSN I in a massive, luminous infrared galaxy at redshift z=0.29, while PTF 10tpz is an SLSN II located in the nucleus of an early-type host at z=0.04. © 2016
âThrough and Throughâ History: The Management of Gunshot Wounds From the 14th Century to the Present
Gun violence killed over 46,000 Americans in 2021; almost 120,000 suffered gunshot wounds. This epidemic has attracted national attention and increasing concern from medical and surgical organizations, as evident in this special issue. âThrough and Through Historyâ explores the surgical management of gunshot wounds from their earliest appearance in 14th-century Europe to the present. Interweaving the civilian and military experience, it details not only the evolution of care directly applied to patients but also the social, political, and scientific milieu that shaped decisions made and actions performed both in and out of the operating room. The article describes how surgeons have pushed the boundaries of medicine and science in each era, developing new therapies for their patients, a historical trend that persists today when such care has the potential to save tens of thousands of lives each year