532 research outputs found
Ambient Salinity and the Daily Variation of Circulating Prolactin in the Gulf Killifish Fundulus grandis
Gulf killifish were maintained in either 3‰ or 35‰ commercial sea salts on a LD 12:12 photoperiod regime and sampled by heart puncture at one of 6 different times of day. Maximum titers of circulating prolactin occurred at the same time of day (8h after light onset) in fish acclimated to either 3‰ or 35‰. Fish acclimated to 3‰ had an additional increase in serum prolactin (8h after light offset) not noted in 35‰ acclimated fish
Effects of Thermocycles on Body Weight Gain and Gonadal Growth in the Goldfish, Carassius auratus
Goldfish subjected to increased temperatures at one of six different times of day had significant differences in weight gain and testicular growth depending on the time of treatment. Depending on the time of day the thermocycle was initiated, weight gain and testicular growth could be either stimulated, inhibited, or equal to that in fishes subjected to constant heat or constant cold. Heat applied during the last 4 h of darkness was particularly conducive to weight gain and testicular growth. The results of this study may have important implications for aquaculture
A HST study of the stellar populations in the cometary dwarf irregular galaxy NGC 2366
We present V and I photometry of the resolved stars in the cometary dwarf
irregular galaxy NGC 2366, using Wide Field Planetary Camera 2 images obtained
with the Hubble Space Telescope. The resulting color-magnitude diagram reaches
down to I~26.0 mag. It reveals not only a young population of blue
main-sequence stars (age <30 Myr) but also an intermediate-age population of
blue and red supergiants (20 Myr<age<100 Myr), and an older evolved populations
of asymptotic giant branch (AGB) stars (age >100 Myr) and red giant branch
(RGB) stars (age >1 Gyr). The measured magnitude I=23.65+/-0.10 mag of the RGB
tip results in a distance modulus m-M=27.67+/-0.10, which corresponds to a
distance of 3.42+/-0.15 Mpc, in agreement with previous distance
determinations. The youngest stars are associated with the bright complex of
HII regions NGC 2363=Mrk 71 in the southwest extremity of the galaxy. As a
consequence of the diffusion and relaxation processes of stellar ensembles, the
older the stellar population is, the smoother and more extended is its spatial
distribution. An underlying population of older stars is found throughout the
body of NGC 2366. The most notable feature of this older population is the
presence of numerous relatively bright AGB stars. The number ratio of AGB to
RGB stars and the average absolute brightness of AGB stars in NGC 2366 are
appreciably higher than in the BCD VII Zw 403, indicating a younger age of the
AGB stars in NGC 2366. In addition to the present burst of age <100 Myr, there
has been strong star formation activity in the past of NGC 2366, from ~100 Myr
to <3 Gyr ago.Comment: 32 pages, 15 figures, accepted for publication in the Astrophysical
Journa
Emission-Line Galaxies from the Hubble Space Telescope Probing Evolution and Reionization Spectroscopically (PEARS) Grism Survey. II: The Complete Sample
We present a full analysis of the Probing Evolution And Reionization
Spectroscopically (PEARS) slitess grism spectroscopic data obtained with the
Advanced Camera for Surveys on HST. PEARS covers fields within both the Great
Observatories Origins Deep Survey (GOODS) North and South fields, making it
ideal as a random survey of galaxies, as well as the availability of a wide
variety of ancillary observations to support the spectroscopic results. Using
the PEARS data we are able to identify star forming galaxies within the
redshift volume 0< z<1.5. Star forming regions in the PEARS survey are
pinpointed independently of the host galaxy. This method allows us to detect
the presence of multiple emission line regions (ELRs) within a single galaxy.
1162 Ha, [OIII] and/or [OII] emission lines have been identified in the PEARS
sample of ~906 galaxies down to a limiting flux of ~1e-18 erg/s/cm^2. The ELRs
have also been compared to the properties of the host galaxy, including
morphology, luminosity, and mass. From this analysis we find three key results:
1) The computed line luminosities show evidence of a flattening in the
luminosity function with increasing redshift; 2) The star forming systems show
evidence of disturbed morphologies, with star formation occurring predominantly
within one effective (half-light) radius. However, the morphologies show no
correlation with host stellar mass; and 3) The number density of star forming
galaxies with M_* > 1e9} M_sun decreases by an order of magnitude at z<0.5
relative to the number at 0.5<z<0.9 in support of the argument for galaxy
downsizing.Comment: Submitted. 48 pages. 19 figures. Accepted to Ap
The Mass-Metallicity and Luminosity-Metallicity Relation from DEEP2 at z ~ 0.8
We present the mass-metallicity (MZ) and luminosity-metallicity (LZ)
relations at z ~ 0.8 from ~1350 galaxies in the Deep Extragalactic Evolutionary
Probe 2 (DEEP2) survey. We determine stellar masses by fitting the spectral
energy distribution inferred from photometry with current stellar population
synthesis models. This work raises the number of galaxies with metallicities at
z ~ 0.8 by more than an order of magnitude. We investigate the evolution in the
MZ and LZ relations in comparison with local MZ and LZ relations determined in
a consistent manner using ~21,000 galaxies in the Sloan Digital Sky Survey. We
show that high stellar mass galaxies (log(M/M_solar)~10.6) at z ~ 0.8 have
attained the chemical enrichment seen in the local universe, while lower
stellar mass galaxies (log(M/M_solar)~9.2) at z ~ 0.8 have lower metallicities
(Delta log(O/H)~0.15 dex) than galaxies at the same stellar mass in the local
universe. We find that the LZ relation evolves in both metallicity and B-band
luminosity between z ~ 0.8 and z~ 0, with the B-band luminosity evolving as a
function of stellar mass. We emphasize that the B-band luminosity should not be
used as a proxy for stellar mass in chemical evolution studies of star-forming
galaxies. Our study shows that both the metallicity evolution and the B-band
luminosity evolution for emission-line galaxies between the epochs are a
function of stellar mass, consistent with the cosmic downsizing scenario of
galaxy evolution.Comment: Accepted Version: 18 pages, 13 figure
AEGIS: Enhancement of Dust-enshrouded Star Formation in Close Galaxy Pairs and Merging Galaxies up to z ~ 1
Using data from the DEEP2 Galaxy Redshift Survey and HST/ACS imaging in the
Extended Groth Strip, we select nearly 100 interacting galaxy systems including
kinematic close pairs and morphologically identified merging galaxies. Spitzer
MIPS 24 micron fluxes of these systems reflect the current dusty star formation
activity, and at a fixed stellar mass (M_{*}) the median infrared luminosity
(L_{IR}) among merging galaxies and close pairs of blue galaxies is twice (1.9
+/- 0.4) that of control pairs drawn from isolated blue galaxies. Enhancement
declines with galaxy separation, being strongest in close pairs and mergers and
weaker in wide pairs compared to the control sample. At z ~ 0.9, 7.1% +/- 4.3%
of massive interacting galaxies (M_{*} > 2*10^{10} M_{solar}) are found to be
ULIRGs, compared to 2.6% +/- 0.7% in the control sample. The large spread of IR
luminosity to stellar mass ratio among interacting galaxies suggests that this
enhancement may depend on the merger stage as well as other as yet unidentified
factors (e.g., galaxy structure, mass ratio, orbital characteristics, presence
of AGN or bar). The contribution of interacting systems to the total IR
luminosity density is moderate (<= 36 %).Comment: 12 pages, 2 figures, 1 table, minor changes to match the proof
version, accepted for publication in the ApJL AEGIS Special Issu
Very Strong Emission-Line Galaxies in the WISP Survey and Implications for High-Redshift Galaxies
The WFC3 Infrared Spectroscopic Parallel Survey (WISP) uses the Hubble Space
Telescope (HST) infrared grism capabilities to obtain slitless spectra of
thousands of galaxies over a wide redshift range including the peak of star
formation history of the Universe. We select a population of very strong
emission-line galaxies with rest-frame equivalent widths higher than 200 A. A
total of 176 objects are found over the redshift range 0.35 < z < 2.3 in the
180 arcmin^2 area we analyzed so far. After estimating the AGN fraction in the
sample, we show that this population consists of young and low-mass starbursts
with higher specific star formation rates than normal star-forming galaxies at
any redshift. After spectroscopic follow-up of one of these galaxies with
Keck/LRIS, we report the detection at z = 0.7 of an extremely metal-poor galaxy
with 12+Log(O/H)= 7.47 +- 0.11. The nebular emission-lines can substantially
affect the broadband flux density with a median brightening of 0.3 mag, with
examples producing brightening of up to 1 mag. The presence of strong emission
lines in low-z galaxies can mimic the color-selection criteria used in the z ~
8 dropout surveys. In order to effectively remove low redshift interlopers,
deep optical imaging is needed, at least 1 mag deeper than the bands in which
the objects are detected. Finally, we empirically demonstrate that strong
nebular lines can lead to an overestimation of the mass and the age of galaxies
derived from fitting of their SED. Without removing emission lines, the age and
the stellar mass estimates are overestimated by a factor of 2 on average and up
to a factor of 10 for the high-EW galaxies. Therefore the contribution of
emission lines should be systematically taken into account in SED fitting of
star-forming galaxies at all redshifts.Comment: Accepted for publication in the Astrophysical Journal. 15 pages, 13
figure
The Persistence of Cool Galactic Winds in High Stellar Mass Galaxies Between z~1.4 and ~1
We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption
line profiles in coadded spectra of 468 galaxies at 0.7 < z < 1.5. The galaxy
sample, drawn from the Team Keck Treasury Redshift Survey of the GOODS-N field,
has a range in stellar mass (M_*) comparable to that of the sample at z~1.4
analyzed in a similar manner by Weiner et al. (2009; W09), but extends to lower
redshifts and has specific star formation rates which are lower by ~0.6 dex. We
identify outflows of cool gas from the Doppler shift of the MgII absorption
lines and find that the equivalent width (EW) of absorption due to outflowing
gas increases on average with M_* and star formation rate (SFR). We attribute
the large EWs measured in spectra of the more massive, higher-SFR galaxies to
optically thick absorbing clouds having large velocity widths. The outflows
have hydrogen column densities N(H) > 10^19.3 cm^-2, and extend to velocities
of ~500 km/s. While galaxies with SFR > 10 Msun/yr host strong outflows in both
this and the W09 sample, we do not detect outflows in lower-SFR (i.e., log
M_*/Msun < 10.5) galaxies at lower redshifts. Using a simple galaxy evolution
model which assumes exponentially declining SFRs, we infer that strong outflows
persist in galaxies with log M_*/Msun > 10.5 as they age between z=1.4 and z~1,
presumably because of their high absolute SFRs. Finally, using high resolution
HST/ACS imaging in tandem with our spectral analysis, we find evidence for a
weak trend (at 1 sigma significance) of increasing outflow absorption strength
with increasing galaxy SFR surface density.Comment: Submitted to ApJ. 25 pages, 19 figures, Figure 2 reduced in
resolution. Uses emulateapj forma
Dependence of Star Formation Activity On Stellar Mass and Environment From the Redshift One LDSS-3 Emission Line Survey (ROLES)
Using the sample from the \it Redshift One LDSS3 Emission line Survey \rm
(ROLES), we probe the dependence of star formation rate (SFR) and specific star
formation rate (sSFR) as a function of stellar mass and environment as
defined by local galaxy density, in the CDFS field. Our spectroscopic sample
consists of 312 galaxies with , corresponding to stellar mass
\log(M_*/M_{\sun})>8.5, and with [OII] derived star-formation rates
SFR>0.3M_{\sun}/yr, at . The results have been
compared directly with the Sloan Digital Sky Survey Stripe 82 sample at
. For star-forming galaxies, we confirm that there is
little correlation between SFR and density at . However, for the
lowest mass galaxies in our sample, those with
\log(M_*/M_{\sun})<10, we find that both the median SFR and specific SFR {\it
increase} significantly with increasing local density. The "downsizing" trend
for low mass galaxies to be quenched progressively later in time appears to be
more pronounced in moderately overdense environments. Overall we find that the
evolution of star-formation in galaxies is most strongly driven by their
stellar mass, with local galaxy density playing a role that becomes
increasingly important for lower mass galaxies.Comment: MNRAS accepte
Environmental Dependence of Local Luminous Infrared Galaxies
We study the environmental dependence of local luminous infrared galaxies
(LIRGs) and ultraluminous infrared galaxies (ULIRGs) found in the Sloan Digital
Sky Survey (SDSS) data. The LIRG and ULIRG samples are constructed by
cross-correlating spectroscopic catalogs of galaxies of the SDSS Data Release 7
and the Infrared Astronomical Satellite Faint Source Catalog. We examine the
effects of the large-scale background density (Sigma_5), galaxy clusters, and
the nearest neighbor galaxy on the properties of infrared galaxies (IRGs). We
find that the fraction of LIRGs plus ULIRGs among IRGs (f_(U)LIRGs) and the
infrared luminosity (L_IR) of IRGs strongly depend on the morphology of and the
distance to the nearest neighbor galaxy: the probability for an IRG to be a
(U)LIRG (f_(U)LIRGs) and its L_IR both increase as it approaches a late-type
galaxy, but decrease as it approaches an early-type galaxy (within half the
virial radius of its neighbor). We find no dependence of f_(U)LIRGs on the
background density (surface galaxy number density) at fixed stellar mass of
galaxies. The dependence of f_(U)LIRGs on the distance to galaxy clusters is
also found to be very weak, but in highest-density regions such as the center
of galaxy clusters, few (U)LIRGs are found. These environmental dependence of
LIRGs and ULIRGs and the evolution of star formation rate (SFR)-environment
relation from high redshifts to low redshifts seem to support the idea that
galaxy-galaxy interactions/merging play a critical role in triggering the star
formation activity of LIRGs and ULIRGs.Comment: 14 pages, 17 figures. To appear in A&A. Paper with high resolution
figures is available at
http://astro.kias.re.kr/~hshwang/doc/ms_hwang_lirg.pd
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