46 research outputs found
Television Scales
How to reckon with the staggering volume of television materials, past and present? And how to comprehend all the potential, complex scales at which to grapple with television, from its tiniest units of audiovisual content to its most massive industrial coordinates and beyond? In Television Scales, Nick Salvato demonstrates how the problem of scale in the field of television may be turned into a resource and a method for a television studies that would pay better attention to messy medial complexities, peripatetic critical practices, and vulgar psychogeographies. Modeling his investigative practice on the meta-critical writing of social anthropologist Marilyn Strathern in Partial Connections and elsewhere, Salvato composes surprising, partial constellations of televisionâs elements. In the process, his consideration ranges from classic television sitcoms like I Love Lucy to contemporary reality series such as The Biggest Loser, Iron Chef, and House Hunters International. He simultaneously pores over a number of key television phenomena, including technological mystification, performersâ charismatic displays, binge viewing, and devoted fandom. An experiment in style and form, Television Scales maps, weighs, and rules television, while also undoing these very strategies for evaluating the medium
The VLA-COSMOS Survey: V. 324 MHz continuum observations
We present 90 cm VLA imaging of the COSMOS field, comprising a circular area
of 3.14 square degrees at 8.0"x6.0" angular resolution with an average rms of
0.5 mJy/beam. The extracted catalog contains 182 sources (down to 5.5sigma), 30
of which are multi-component sources. Using Monte Carlo artificial source
simulations we derive the completeness of the catalog, and we show that our 90
cm source counts agree very well with those from previous studies. Using X-ray,
NUV-NIR and radio COSMOS data to investigate the population mix of our 90 cm
radio sample, we find that our sample is dominated by active galactic nuclei
(AGN). The average 90-20 cm spectral index (S_nu~nu**alpha, where S_nu is the
flux density at frequency nu, and alpha the spectral index) of our 90 cm
selected sources is -0.70, with an interquartile range of -0.90 to -0.53. Only
a few ultra-steep-spectrum sources are present in our sample, consistent with
results in the literature for similar fields. Our data do not show clear
steepening of the spectral index with redshift. Nevertheless, our sample
suggests that sources with spectral indices steeper than -1 all lie at z>1, in
agreement with the idea that ultra-steep-spectrum radio sources may trace
intermediate-redshift galaxies (z>1).Comment: 10 pages, 12 figures, accepted for publication in MNRA
Encoding the infrared excess (IRX) in the NUVrK color diagram for star-forming galaxies
We present an empirical method of assessing the star formation rate (SFR) of
star-forming galaxies based on their locations in the rest-frame color-color
diagram (NUV-r) vs (r-K). By using the Spitzer 24 micron sample in the COSMOS
field (~16400 galaxies with 0.2 < z < 1.3) and a local GALEX-SDSS-SWIRE sample
(~700 galaxies with z = <
L_IR / L_UV > can be described by a single vector, NRK, that combines the two
colors. The calibration between and NRK allows us to recover the IR
luminosity, L_IR, with an accuracy of ~0.21 dex for the COSMOS sample and ~0.27
dex for the local one. The SFRs derived with this method agree with the ones
based on the observed (UV+IR) luminosities and on the spectral energy
distribution fitting for the vast majority (~85 %) of the star-forming
population. Thanks to a library of model galaxy SEDs with realistic
prescriptions for the star formation history, we show that we need to include a
two-component dust model (i.e., birth clouds and diffuse ISM) and a full
distribution of galaxy inclinations in order to reproduce the behavior of the
stripes in the NUVrK diagram. In conclusion, the NRK method, based only
on rest-frame UV and optical colors available in most of the extragalactic
fields, offers a simple alternative of assessing the SFR of star-forming
galaxies in the absence of far-IR or spectral diagnostic observations.Comment: 21 pages, 22 figures, in publication in Astronomy & Astrophysic
Observational limits on type 1 active galactic nucleus rate in COSMOS
We present black hole masses and accretion rates for 182 Type 1 active galactic nuclei (AGNs) in COSMOS.
We estimate masses using the scaling relations for the broad H ÎČ, Mg ii, and C iv emission lines in the
redshift ranges 0.16 < z < 0.88, 1 < z < 2.4, and 2.7 < z < 4.9. We estimate the accretion rate using an
Eddington ratio LI/L_(Edd) estimated from optical and X-ray data.We find that very few Type 1 AGNs accrete below
LI/L_(Edd) ⌠0.01, despite simulations of synthetic spectra which show that the survey is sensitive to such Type
1 AGNs. At lower accretion rates the broad-line region may become obscured, diluted, or nonexistent. We find
evidence that Type 1 AGNs at higher accretion rates have higher optical luminosities, as more of their emission
comes from the cool (optical) accretion disk with respect to shorter wavelengths. We measure a larger range
in accretion rate than previous works, suggesting that COSMOS is more efficient at finding low accretion rate
Type 1 AGNs. However, the measured range in accretion rate is still comparable to the intrinsic scatter from the
scaling relations, suggesting that Type 1 AGNs accrete at a narrow range of Eddington ratio, with LI/L_(Edd) ⌠0.1
Relation Between Stellar Mass and Star Formation Activity in Galaxies
For a mass-selected sample of 66544 galaxies with photometric redshifts from
the Cosmic Evolution Survey (COSMOS), we examine the evolution of star
formation activity as a function of stellar mass in galaxies. We estimate the
cosmic star formation rates (SFR) over the range 0.2 < z < 1.2, using the
rest-frame 2800 A flux (corrected for extinction). We find the mean SFR to be a
strong function of the galactic stellar mass at any given redshift, with
massive systems (log (M/M(Sun)) > 10.5) contributing less (by a factor of ~ 5)
to the total star formation rate density (SFRD).
Combining data from the COSMOS and Gemini Deep Deep Survey (GDDS), we extend
the SFRD-z relation as a function of stellar mass to z~2. For massive galaxies,
we find a steep increase in the SFRD-z relation to z~2; for the less massive
systems, the SFRD which also increases from z=0 to 1, levels off at z~1. This
implies that the massive systems have had their major star formation activity
at earlier epochs (z > 2) than the lower mass galaxies.
We study changes in the SFRDs as a function of both redshift and stellar mass
for galaxies of different spectral types. We find that the slope of the SFRD-z
relation for different spectral type of galaxies is a strong function of their
stellar mass. For low and intermediate mass systems, the main contribution to
the cosmic SFRD comes from the star-forming galaxies while, for more massive
systems, the evolved galaxies are the most dominant population.Comment: 34 pages; 8 figures; Accepted for publication in Ap
Observational Limits on Type 1 AGN Accretion Rate in COSMOS
We present black hole masses and accretion rates for 182 Type 1 AGN in
COSMOS. We estimate masses using the scaling relations for the broad Hb, MgII,
and CIV emission lines in the redshift ranges 0.16<z<0.88, 1<z<2.4, and
2.7<z<4.9. We estimate the accretion rate using an Eddington ratio L_I/L_Edd
estimated from optical and X-ray data. We find that very few Type 1 AGN accrete
below L_I/L_Edd ~ 0.01, despite simulations of synthetic spectra which show
that the survey is sensitive to such Type 1 AGN. At lower accretion rates the
BLR may become obscured, diluted or nonexistent. We find evidence that Type 1
AGN at higher accretion rates have higher optical luminosities, as more of
their emission comes from the cool (optical) accretion disk with respect to
shorter wavelengths. We measure a larger range in accretion rate than previous
works, suggesting that COSMOS is more efficient at finding low accretion rate
Type 1 AGN. However the measured range in accretion rate is still comparable to
the intrinsic scatter from the scaling relations, suggesting that Type 1 AGN
accrete at a narrow range of Eddington ratio, with L_I/L_Edd ~ 0.1.Comment: Accepted for pulication in ApJ. 7 pages, 5 figures, table 1 available
on reques
Massive Galaxies in COSMOS: Evolution of Black hole versus bulge mass but not versus total stellar mass over the last 9 Gyrs?
We constrain the ratio of black hole (BH) mass to total stellar mass of
type-1 AGN in the COSMOS survey at 1<z<2. For 10 AGN at mean redshift z~1.4
with both HST/ACS and HST/NICMOS imaging data we are able to compute total
stellar mass M_(*,total), based on restframe UV-to-optical host galaxy colors
which constrain mass-to-light ratios. All objects have virial BH mass-estimates
available from the COSMOS Magellan/IMACS and zCOSMOS surveys. We find zero
difference between the M_BH--M_(*,total)-relation at z~1.4 and the
M_BH--M_(*,bulge)-relation in the local Universe.
Our interpretation is: (a) If our objects were purely bulge-dominated, the
M_BH--M_(*,bulge)-relation has not evolved since z~1.4. However, (b) since we
have evidence for substantial disk components, the bulges of massive galaxies
(logM_(*,total)=11.1+-0.25 or logM_BH~8.3+-0.2) must have grown over the last 9
Gyrs predominantly by redistribution of disk- into bulge-mass. Since all
necessary stellar mass exists in the galaxy at z=1.4, no star-formation or
addition of external stellar material is required, only a redistribution e.g.
induced by minor and major merging or through disk instabilities. Merging, in
addition to redistributing mass in the galaxy, will add both BH and
stellar/bulge mass, but does not change the overall final M_BH/M_(*,bulge)
ratio.
Since the overall cosmic stellar and BH mass buildup trace each other tightly
over time, our scenario of bulge-formation in massive galaxies is independent
of any strong BH-feedback and means that the mechanism coupling BH and bulge
mass until the present is very indirect.Comment: Published in ApJL; 7 pages, 2 figures; updated to accepted version
(methods changed, results unchanged
The bulk of the black hole growth since z ~ 1 occurs in a secular universe: no major merger-AGN connection
What is the relevance of major mergers and interactions as triggering mechanisms for active galactic nuclei (AGNs)
activity? To answer this long-standing question, we analyze 140 XMM-Newton-selected AGN host galaxies and
a matched control sample of 1264 inactive galaxies over z ~ 0.3â1.0 and M_â < 10^(11.7) M_â with high-resolution
Hubble Space Telescope/Advanced Camera for Surveys imaging from the COSMOS field. The visual analysis of
their morphologies by 10 independent human classifiers yields a measure of the fraction of distorted morphologies
in the AGN and control samples, i.e., quantifying the signature of recent mergers which might potentially be
responsible for fueling/triggering the AGN. We find that (1) the vast majority (>85%) of the AGN host galaxies
do not show strong distortions and (2) there is no significant difference in the distortion fractions between active
and inactive galaxies. Our findings provide the best direct evidence that, since z ~ 1, the bulk of black hole (BH)
accretion has not been triggered by major galaxy mergers, therefore arguing that the alternative mechanisms, i.e.,
internal secular processes and minor interactions, are the leading triggers for the episodes of major BH growth.We
also exclude an alternative interpretation of our results: a substantial time lag between merging and the observability
of the AGN phase could wash out the most significant merging signatures, explaining the lack of enhancement
of strong distortions on the AGN hosts. We show that this alternative scenario is unlikely due to (1) recent major
mergers being ruled out for the majority of sources due to the high fraction of disk-hosted AGNs, (2) the lack of
a significant X-ray signal in merging inactive galaxies as a signature of a potential buried AGN, and (3) the low
levels of soft X-ray obscuration for AGNs hosted by interacting galaxies, in contrast to model predictions
Star Formation at From the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH)
Using the first 50% of data collected for the Spitzer Large Area Survey with
Hyper-Suprime-Cam (SPLASH) observations on the 1.8 deg Cosmological
Evolution Survey (COSMOS) we estimate the masses and star formation rates of
3398 star-forming galaxies at with a
substantial population up to . We find that the
strong correlation between stellar mass and star formation rate seen at lower
redshift (the "main sequence" of star-forming galaxies) extends to .
The observed relation and scatter is consistent with a continued increase in
star formation rate at fixed mass in line with extrapolations from
lower-redshift observations. It is difficult to explain this continued
correlation, especially for the most massive systems, unless the most massive
galaxies are forming stars near their Eddington-limited rate from their first
collapse. Furthermore, we find no evidence for moderate quenching at higher
masses, indicating quenching either has not occurred prior to or
else occurs rapidly, so that few galaxies are visible in transition between
star-forming and quenched.Comment: ApJL, accepte
The Nature of Optically Dull Active Galactic Nuclei in COSMOS
We present infrared, optical, and X-ray data of 48 X-ray bright, optically
dull AGNs in the COSMOS field. These objects exhibit the X-ray luminosity of an
active galactic nucleus (AGN) but lack broad and narrow emission lines in their
optical spectrum. We show that despite the lack of optical emission lines, most
of these optically dull AGNs are not well-described by a typical passive red
galaxy spectrum: instead they exhibit weak but significant blue emission like
an unobscured AGN. Photometric observations over several years additionally
show significant variability in the blue emission of four optically dull AGNs.
The nature of the blue and infrared emission suggest that the optically
inactive appearance of these AGNs cannot be caused by obscuration intrinsic to
the AGNs. Instead, up to ~70% of optically dull AGNs are diluted by their
hosts, with bright or simply edge-on hosts lying preferentially within the
spectroscopic aperture. The remaining ~30% of optically dull AGNs have
anomalously high f_x/f_o ratios and are intrinsically weak, not obscured, in
the optical. These optically dull AGNs are best described as a weakly accreting
AGN with a truncated accretion disk from a radiatively inefficient accretion
flow.Comment: 12 pages, 10 figures. Accepted for publication in the Ap