860 research outputs found
Optical Spectroscopy of K-selected Extremely Red Galaxies
We have obtained spectroscopic redshifts for 24 red galaxies from a sample
with median Ks=18.7 and F814W - Ks > 4, using the Keck telescope. These
EROshave high resolution morphologies from HST (Yan & Thompson 2003). Among the
24 redshifts, the majority (92%) are at . We derived the
rest-frame J-band luminosity function at . Our result
suggests that the luminosity evolution between bright EROs at and the
present-day L massive galaxies is at most about 0.7 magnitude. Combining
the morphologies and deep spectroscopy revealed the following properties: (1)
86% of the spectra have absorption features from old stars, suggesting that the
dominant stellar populations seen in the rest-frame UV are old stars. 50% of
the sources have pure absorption lines, while the remaining 50% have emission
lines, indicating recent star formation. We conclude that the color criterion
for EROs is very effective in selecting old stellar populations at ,
and a large fraction of these systems with prominent old stellar populations
also have recent star formation. (2) The 12 emission line systems have the same
number of disk and bulge galaxies as in the remaining 12 pure absorption line
systems. We conclude that spectral classes do not have a simple, direct
correspondence with morphological types. (3) Three EROs could be isolated, pure
passively evolving early-type galaxies at . This implies that only a
small fraction (10%--15%) of early-type galaxies are formed in a rapid burst of
star formation at high redshifts and evolved passively since then. (Abridged).Comment: 27 pages, 8 figures. Accepted for publication in Astronomical
Journal, issue March 200
The contribution of starbursts and normal galaxies to infrared luminosity functions at z < 2
We present a parameter-less approach to predict the shape of the infrared
(IR) luminosity function (LF) at redshifts z < 2. It requires no tuning and
relies on only three observables: (1) the redshift evolution of the stellar
mass function for star-forming galaxies, (2) the evolution of the specific star
formation rate (sSFR) of main-sequence galaxies, and (3) the double-Gaussian
decomposition of the sSFR-distribution at fixed stellar mass into a
contribution (assumed redshift- and mass-invariant) from main-sequence and
starburst activity. This self-consistent and simple framework provides a
powerful tool for predicting cosmological observables: observed IR LFs are
successfully matched at all z < 2, suggesting a constant or only weakly
redshift-dependent contribution (8-14%) of starbursts to the star formation
rate density. We separate the contributions of main-sequence and starburst
activity to the global IR LF at all redshifts. The luminosity threshold above
which the starburst component dominates the IR LF rises from log(LIR/Lsun) =
11.4 to 12.8 over 0 < z < 2, reflecting our assumed (1+z)^2.8-evolution of sSFR
in main-sequence galaxies.Comment: 7 pages, 4 figures & 1 table. Accepted for publication in ApJL. Minor
typos corrected in v2 following receipt of proof
Near-IR bright galaxies at z~2. Entering the spheroid formation epoch ?
Spectroscopic redshifts have been measured for 9 K-band luminous galaxies at
1.7 < z < 2.3, selected with Ks < 20 in the "K20 survey" region of the Great
Observatories Origins Deep Survey area. Star formation rates (SFRs) of ~100-500
Msun/yr are derived when dust extinction is taken into account. The fitting of
their multi-color spectral energy distributions indicates stellar masses M ~
10^11 Msun for most of the galaxies. Their rest-frame UV morphology is highly
irregular, suggesting that merging-driven starbursts are going on in these
galaxies. Morphologies tend to be more compact in the near-IR, a hint for the
possible presence of older stellar populations. Such galaxies are strongly
clustered, with 7 out of 9 belonging to redshift spikes, which indicates a
correlation length r_0 ~ 9-17 h^-1 Mpc (1 sigma range). Current semianalytical
models of galaxy formation appear to underpredict by a large factor (about 30)
the number density of such a population of massive and powerful starburst
galaxies at z ~ 2. The high masses and SFRs together with the strong clustering
suggest that at z ~ 2 we may have started to explore the major formation epoch
of massive early-type galaxies.Comment: accepted on June 17. To appear on ApJ Letter
The Subillimeter Properties of Extremely Red Objects in the CUDSS Fields
We discuss the submillimeter properties of Extremely Red Objects (EROs) in
the two Canada-UK Deep Submillimeter Survey (CUDSS) Fields. We measure the mean
submillimeter flux of the ERO population (to K < 20.7) and find 0.4 +/- 0.07
mJy for EROs selected by (I-K) > 4.0 and 0.56 +/- 0.09 mJy for EROs selected by
(R-K) > 5.3 but, these measurements are dominated by discrete, bright
submillimeter sources. We estimate that EROs produce 7-11% of the far-infrared
background at 850um. This is substantially less than a previous measurement by
Wehner, Barger & Kneib (2002) and we discuss possible reasons for this
discrepancy. We show that ERO counterparts to bright submillimeter sources lie
within the starburst region of the near-infrared color-color plot of Pozzetti &
Mannucci (2000). Finally, we claim that pairs or small groups of EROs with
separations of < 10 arcseconds often mark regions of strong submillimeter flux.Comment: 9 pages, 8 figures, accepted for publication in Ap
A wide area survey for high-redshift massive galaxies. I. Number counts and clustering of BzKs and EROs
We have combined deep BRIz' imaging over 2x940 arcmin^2 fields obtained with
the Suprime-Cam on the Subaru telescope with JKs imaging with the SOFI camera
at the New Technology Telescope to search for high-redshift massive galaxies.
K-band selected galaxies have been identified over an area of ~920 arcmin^2 to
K_Vega=19.2, of which 320 arcmin^2 are complete to K_Vega=20. The BzK selection
technique was used to obtain complete samples of ~500 candidate massive
star-forming galaxies (sBzKs) and ~160 candidate massive, passively-evolving
galaxies (pBzKs), both at 1.4 5 criterion we also
identified ~850 extremely red objects (EROs). The surface density of sBzKs and
pBzKs is found to 1.20+/-0.05 arcmin^{-2} and 0.38+/-0.03 arcmin^{-2},
respectively. Both sBzKs and pBzKs are strongly clustered, at a level at least
comparable to that of EROs, with pBzKs appearing more clustered than sBzKs. We
estimate the reddening, star formation rates (SFRs) and stellar masses (M_*) of
the sBzKs, confirming that to K_Vega~20 median values are M_*~10^{11}M_sun, SFR
190M_sun yr^{-1}, and E(B-V)~0.44. The most massive sBzKs are also the most
actively star-forming, an effect which can be seen as a manifestation of
downsizing at early epochs. The space density of massive pBzKs at z~1.4-2 is
20%+/-7% that of similarly massive early-type galaxies at z~0, and similar to
that of sBzKs of the same mass. We argue that star formation quenching in these
sBzKs will result in nearly doubling the space density of massive early-type
galaxies, thus matching their local density.Comment: 19 pages, 13 figures, accepted by ApJ. While checking the proofs we
became aware of a material mistake of non-trivial scientific relevance. In
the original it was reported that the comoving volume density of passive
BzK-selected galaxies with =1.7 and more massive than 10^{11}M_sun was
45%+/-15% of the local number density of similarly massive early-type
galaxies. This fraction actually turns out to be 20%+/-7%. Section 6.4, point
5 in section 7, and the abstract have been modified accordingl
The contribution of starbursts and normal galaxies to IR luminosity functions and the molecular gas content of the Universe at z<2
We present a parameter-less approach capable of predicting
the shape of the infrared luminosity function at redshifts z ≤2. It relies on
three observables: (1) the redshift evolution of the stellar mass function
for star-forming galaxies, (2) the evolution of the specific star formation
rate of main-sequence galaxies, and (3) the double-Gaussian decomposition
of the specific star formation rate distribution at fixed stellar mass
into the contributions (assumed to be redshift- and mass-invariant) from
main-sequence and starburst activity.
Using this self-consistent and simple framework, we identify the contributions
of main-sequence and starburst activity to the global infrared luminosity
function and find a constant or only weakly redshift-dependent
contribution (8–14%) of starbursts to the star formation rate density at
z ≤2. Over the same redshift range, we also infer the evolution of the
cosmic abundance of molecular gas in star-forming galaxies, based on the
relations between star formation rate and molecular gas mass followed by
normal and starburst galaxies
Hydrodynamic coupling and rotational mobilities near planar elastic membranes
We study theoretically and numerically the coupling and rotational
hydrodynamic interactions between spherical particles near a planar elastic
membrane that exhibits resistance towards shear and bending. Using a
combination of the multipole expansion and Faxen's theorems, we express the
frequency-dependent hydrodynamic mobility functions as a power series of the
ratio of the particle radius to the distance from the membrane for the self
mobilities, and as a power series of the ratio of the radius to the
interparticle distance for the pair mobilities. In the quasi-steady limit of
zero frequency, we find that the shear- and bending-related contributions to
the particle mobilities may have additive or suppressive effects depending on
the membrane properties in addition to the geometric configuration of the
interacting particles relative to the confining membrane. To elucidate the
effect and role of the change of sign observed in the particle self and pair
mobilities, we consider an example involving a torque-free doublet of
counterrotating particles near an elastic membrane. We find that the induced
rotation rate of the doublet around its center of mass may differ in magnitude
and direction depending on the membrane shear and bending properties. Near a
membrane of only energetic resistance toward shear deformation, such as that of
a certain type of elastic capsules, the doublet undergoes rotation of the same
sense as observed near a no-slip wall. Near a membrane of only energetic
resistance toward bending, such as that of a fluid vesicle, we find a reversed
sense of rotation. Our analytical predictions are supplemented and compared
with fully resolved boundary integral simulations where a very good agreement
is obtained over the whole range of applied frequencies.Comment: 14 pages, 7 figures. Revised manuscript resubmitted to J. Chem. Phy
Evidence for Infrared-Faint Radio Sources as z > 1 Radio-Loud AGN
Infrared-Faint Radio Sources (IFRSs) are a class of radio objects found in
the Australia Telescope Large Area Survey (ATLAS) which have no observable
mid-infrared counterpart in the Spitzer Wide-area Infrared Extragalactic
(SWIRE) survey. The extended Chandra Deep Field South now has even deeper
Spitzer imaging (3.6 to 70 micron) from a number of Legacy surveys. We report
the detections of two IFRS sources in IRAC images. The non-detection of two
other IFRSs allows us to constrain the source type. Detailed modeling of the
SED of these objects shows that they are consistent with high redshift (z > 1)
AGN.Comment: 10 pages, 7 figures, accepted for publication in Ap
The influence of institutional pressures on climate mitigation and adaptation strategies
Starting from institutional theory, this study aims to explore the effects of coercive, normative and mimetic pressures on businesses climate change mitigation and adaptation strategies. In order to test these hypotheses, the study relies on an econometric model by using data from 487 Italian manufacturing companies collected by a questionnaire-based survey. The empirical model based on a multivariate regression reveals that companies which perceive normative and mimetic pressures are more likely to have a higher climate change sensitivity. Moreover, companies with a higher climate change sensitivity are more likely to adopt both mitigation and adaptation strategies. The article provides several contributions. First the study contributes to the debate among institutional scholars by clarifying which institutional pressures exert a more incisive effect on pushing companies to adopt climate actions. Second, it highlights how internal factors play a mediating role between institutional pressures and business climate responses
Hyper Extremely Red Objects in the Subaru Deep Field: Evidence for Primordial Elliptical Galaxies in the Dusty Starburst Phase
We report observational analyses and theoretical interpretations of unusually
red galaxies in the Subaru Deep Field (SDF). A careful analysis of the SDF data
revealed a population with unusually red near-infrared (NIR) colors of J - K >~
3-4, with higher confidence than the previous SDF result. Their surface number
density drastically increases at K >~ 22 and becomes roughly the same with that
of dusty starburst galaxies detected by submillimeter observations in recent
years. These colors are even redder than the known population of the extremely
red objects (EROs), and too red to explain by passively evolving elliptical
galaxies which are the largest population of EROs. Hence these hyper extremely
red objects (HEROs) should be considered as a distinct population from EROs. We
discuss several possible interpretations of these enigmatic objects, and we
show that these red NIR colors, K-band and sub-mm flux, and surface number
density are quantitatively best explained by primordial elliptical galaxies
reddened by dust, still in the starburst phase of their formation at z ~ 3.Comment: Accepted by ApJ Letter
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