117 research outputs found
Lyman Alpha Emitters in the Hierarchically Clustering Galaxy Formation
We present a new theoretical model for the luminosity functions (LFs) of
Lyman alpha (Lya) emitting galaxies in the framework of hierarchical galaxy
formation. We extend a semi-analytic model of galaxy formation that reproduces
a number of observations for local and high-z galaxies, without changing the
original model parameters but introducing a physically-motivated modelling to
describe the escape fraction of Lya photons from host galaxies (f_esc). Though
a previous study using a hierarchical clustering model simply assumed a
constant and universal value of f_esc, we incorporate two new effects on f_esc:
extinction by interstellar dust and galaxy-scale outflow induced as a star
formation feedback. It is found that the new model nicely reproduces all the
observed Lya LFs of the Lya emitters (LAEs) at different redshifts in z ~ 3-6.
Especially, the rather surprisingly small evolution of the observed LAE Lya LFs
compared with the dark halo mass function is naturally reproduced. Our model
predicts that galaxies with strong outflows and f_esc ~ 1 are dominant in the
observed LFs. This is also consistent with available observations, while the
simple universal f_esc model requires f_esc << 1 not to overproduce the
brightest LAEs. On the other hand, we found that our model significantly
overpredicts LAEs at z > 6, and absorption of Lya photons by neutral hydrogen
in intergalactic medium (IGM) is a reasonable interpretation for the
discrepancy. This indicates that the IGM neutral fraction x_HI rapidly evolves
from x_HI << 1 at z < 6 to a value of order unity at z ~ 6-7, which is broadly
consistent with other observational constraints on the reionization history.Comment: 14 pages, 7 figures, 1 table; accepted to ApJ; the html abstract is
replaced to match the accepted version, the .ps and .pdf files are strictly
identical between the 2nd and the 3rd version
Gradients of absorption-line strengths in elliptical galaxies
© 1999. The American Astronomical Society. All rights reserved. This is the final published version of the work, which was originally published at https://doi.org/10.1086/308092We have restudied line-strength gradients of 80 elliptical galaxies. Typical metallicity gradients of elliptical galaxies are Delta[Fe/H]/Delta log r similar or equal to -0.3, which is flatter than the gradients predicted by monolithic collapse simulations. The metallicity gradients do not correlate with any physical properties of galaxies, including central and mean metallicities, central velocity dispersions sigma(0), absolute B magnitudes M-B, absolute effective radii R-e, and dynamical masses of galaxies. By using the metallicity gradients, we have calculated mean stellar metallicities for individual ellipticals. Typical mean stellar metallicities are [[Fe/H]] similar or equal to -0.3 and range from [[Fe/H]] similar or equal to -0.8 to +0.3, which is contrary to what Gonzalez & Gorgas claimed; the mean metallicities of ellipticals are not universal. The mean metallicities correlate well with sigma(0) and dynamical masses, though relations for M-B and R-e include significant scatters. We find fundamental planes defined by surface brightnesses SBe, [[Fe/H]], and R-e (or M-B), the scatters of which are much smaller than those of the [[Fe/H]]-R-e (or [[Fe/H]]-M-B) relations. The [[Fe/H]]-log sigma(0) relation is nearly parallel to the [Fe/H](0)-log sigma(0) relation but systematically lower by 0.3 dex; thus the mean metallicities are about one-half of the central values. The metallicity-mass relation or, equivalently, the color-magnitude relation of ellipticals holds not only for the central parts of galaxies but also for entire galaxies. Assuming that Mg-2 and Fe-1 give [Mg/H] and [Fe/H], respectively, we find [[Mg/Fe]] similar or equal to +0.2 in most of elliptical galaxies. [[Mg/Fe]] shows no correlation with galaxy mass tracers such as sigma(0), in contrast to what was claimed for the central [Mg/Fe]. This can be most naturally explained if the star formation had stopped in elliptical galaxies before the bulk of Type Ia supernovae began to occur. Elliptical galaxies can have significantly different metallicity gradients and [[Fe/H]], even if they have the same galaxy mass. This may result from galaxy mergers, but no evidence is found from presently available data to support the same origin for metallicity gradients, the scatters around the metallicity-mass relation, and dynamical disturbances. This may suggest that the scatters have their origin at the formation epoch of galaxies.Peer reviewe
The Subaru COSMOS 20: Subaru Optical Imaging of the HST COSMOS Field with 20 Filters
We present both the observations and the data reduction procedures of the
Subaru COSMOS 20 project that is an optical imaging survey of the HST COSMOS
field, carried out by using Suprime-Cam on the Subaru Telescope with the
following 20 optical filters: 6 broad-band (B, g', V, r', i', and z'), 2
narrow-band (NB711 and NB816), and 12 intermediate-band filters (IA427, IA464,
IA484, IA505, IA527, IA574, IA624, IA679, IA709, IA738, IA767, and IA827). A
part of this project is described in Taniguchi et al. (2007) and Capak et al.
(2007) for the six broad-band and one narrow-band (NB816) filter data. In this
paper, we present details of the observations and data reduction for remaining
13 filters (the 12 IA filters and NB711). In particular, we describe the
accuracy of both photometry and astrometry in all the filter bands. We also
present optical properties of the Suprime-Cam IA filter system in Appendix.Comment: 15 pages, 8 figures, 7 tables; accepted for publication in PASJ on
October 2, 201
A Shock-Induced Pair of Superbubbles in the High-Redshift Powerful Radio Galaxy MRC 0406-244
We present new optical spectroscopy of the high-redshift powerful radio
galaxy MRC 0406244 at redshift of 2.429. We find that the two extensions
toward NW and SE probed in the rest-frame ultraviolet image are heated mainly
by the nonthermal continuum of the active galactic nucleus. However, each
extension shows a shell-like morphology, suggesting that they are a pair of
superbubbles induced by the superwind activity rather than by the interaction
between the radio jet and the ambient gas clouds. If this is the case, the
intense starburst responsible for the formation of superbubbles could occur
yr ago. On the other hand, the age of the radio jets may
be of the order of yr, being much shorter than the starburst age.
Therefore, the two events, i.e., the starburst and the radio-jet activities,
are independent phenomena. However, their directions of the expanding motions
could be governed by the rotational motion of the gaseous component in the host
galaxy. This idea appears to explain the alignment effect of MRC 0406244.Comment: 4 pages (emulateapj.sty), Fig. 1 (jpeg) + Fig.2 (eps). Accepted for
publications in ApJ (Letters
Formation and Evolution of Early-Type Galaxies: Spectro-Photometry from Cosmo-Chemo-Dynamical Simulations
One of the major challenges in modern astrophysics is to understand the
origin and the evolution of galaxies, the bright, massive early type galaxies
(ETGs) in particular. Therefore, these galaxies are likely to be good probes of
galaxy evolution, star formation and, metal enrichment in the early Universe.
In this context it is very important to set up a diagnostic tool able to
combine results from chemo-dynamical N-Body-TSPH (NB-TSPH) simulations of ETGs
with those of spectro-photometric population synthesis and evolution so that
all key properties of galaxies can be investigated. The main goal of this paper
is to provide a preliminary validation of the software package before applying
it to the analysis of observational data. The galaxy models in use where
calculated by the Padova group in two different cosmological scenarios: the
SCDM, and the Lambda CDM. For these models, we recover their
spectro-photometric evolution through the entire history of the Universe. We
computed magnitudes and colors and their evolution with the redshift along with
the evolutionary and cosmological corrections for the model galaxies at our
disposal, and compared them with data for ETGs taken from the COSMOS and the
GOODS databases. Starting from the dynamical simulations and photometric models
at our disposal, we created synthetic images from which we derived the
structural and morphological parameters. The theoretical results are compared
with observational data of ETGs selected form the SDSS database. The simulated
colors for the different cosmological scenarios follow the general trend shown
by galaxies of the COSMOS and GOODS. Within the redshift range considered, all
the simulated colors reproduce the observational data quite well.Comment: 28 pages, 28 figures, accepted for pubblication by A&
Stellar population and dust extinction in an ultraluminous infrared galaxy at z=1.135
We present the detailed optical to far-infrared observations of SST
J1604+4304, an ULIRG at z = 1.135. Analyzing the stellar absorption lines,
namely, the CaII H & K and Balmer H lines in the optical spectrum, we derive
the upper limits of an age for the stellar population. Given this constraint,
the minimum {chi}^2 method is used to fit the stellar population models to the
observed SED from 0.44 to 5.8um. We find the following properties. The stellar
population has an age 40 - 200 Myr with a metallicity 2.5 Z_{sun}. The
starlight is reddened by E(B-V) = 0.8. The reddening is caused by the
foreground dust screen, indicating that dust is depleted in the starburst site
and the starburst site is surrounded by a dust shell. The infrared (8-1000um)
luminosity is L_{ir} = 1.78 +/- 0.63 * 10^{12} L_{sun}. This is two times
greater than that expected from the observed starlight, suggesting either that
1/2 of the starburst site is completely obscured at UV-optical wavelengths, or
that 1/2 of L_{ir} comes from AGN emission. The inferred dust mass is 2.0 +/-
1.0 * 10^8 M_{sun}. This is sufficient to form a shell surrounding the galaxy
with an optical depth E(B-V) = 0.8. From our best stellar population model - an
instantaneous starburst with an age 40 Myr, we infer the rate of 19
supernovae(SNe) per year. Simply analytical models imply that 2.5 Z_{sun} in
stars was reached when the gas mass reduced to 30% of the galaxy mass. The gas
metallcity is 4.8 Z_{sun} at this point. The gas-to-dust mass ratio is then 120
+/- 73. The inferred dust production rate is 0.24 +/- 0.12 M_{sun} per SN. If
1/2 of L_{ir} comes from AGN emission, the rate is 0.48 +/- 0.24 M_{sun} per
SN. We discuss the evolutionary link of SST J1604+4304 to other galaxy
populations in terms of the stellar masses and the galactic winds.Comment: 11 pages, 9 figures, accepted for publication in MNRA
Cosmic evolution of the CIV in high-resolution hydrodynamic simulations
We investigate the properties of triply ionized Carbon (CIV) in the
Intergalactic Medium using a set of high-resolution and large box-size
cosmological hydrodynamic simulations of a CDM model. We rely on a
modification of the GADGET-2 code that self-consistently follows the metal
enrichment mechanism by means of a detailed chemical evolution model. We focus
on several numerical implementations of galactic feedback: galactic winds in
the energy driven and momentum driven prescriptions and Active Galactic Nuclei
(AGN) powered by gas accretion onto massive black holes. We extract mock IGM
transmission spectra in neutral hydrogen (HI) and CIV and perform Voigt profile
fitting. The results are then compared with high-resolution quasar (QSO)
spectra obtained with the UVES spectrograph at the VLT and the HIRES
spectrograph at Keck. We find that feedback has little impact on statistics
related to the neutral hydrogen, while CIV is more affected by galactic winds
and/or AGN feedback. When the same analysis is performed over observed and
simulated CIV lines, we find reasonables good agreement between data and
simulations over the column density range cm. Also the CIV line-widths distribution appears
to be in agreement with the observed values, while the HI Doppler parameters,
, are in general too large showing that the diffuse cosmic web is
heated more than what is inferred by observations. The simulation without
feedback fails in reproducing the CIV systems at high column densities at all
redshift, while the AGN feedback case agrees with observations only at ,
when this form of feedback is particularly effective. We also present scatter
plots in the and in the planes, showing that
there is rough agreement between observations and simulations only when
feedback is taken into account.Comment: 22 pages, 20 figures, minor revisions, accepted for publication in
MNRA
Chemical enrichment of galaxy clusters from hydrodynamical simulations
We present cosmological hydrodynamical simulations of galaxy clusters aimed
at studying the process of metal enrichment of the intra--cluster medium (ICM).
These simulations have been performed by implementing a detailed model of
chemical evolution in the Tree-SPH \gd code. This model allows us to follow the
metal release from SNII, SNIa and AGB stars, by properly accounting for the
lifetimes of stars of different mass, as well as to change the stellar initial
mass function (IMF), the lifetime function and the stellar yields. As such, our
implementation of chemical evolution represents a powerful instrument to follow
the cosmic history of metal production. The simulations presented here have
been performed with the twofold aim of checking numerical effects, as well as
the impact of changing the model of chemical evolution and the efficiency of
stellar feedback.Comment: to appear on MNRA
- âŠ