1,416 research outputs found
A Magnified View of the Kinematics and Morphology of RCSGA 032727-132609: Zooming in on a Merger at z=1.7
We present a detailed analysis of multi-wavelength HST/WFC3 imaging and
Keck/OSIRIS near-IR AO-assisted integral field spectroscopy for a highly
magnified lensed galaxy at z=1.70. This young starburst is representative of
UV-selected star-forming galaxies (SFG) at z~2 and contains multiple individual
star-forming regions. Due to the lensing magnification, we can resolve spatial
scales down to 100pc in the source plane of the galaxy. The velocity field
shows disturbed kinematics suggestive of an ongoing interaction, and there is a
clear signature of a tidal tail. We constrain the age, reddening, SFR and
stellar mass of the star-forming clumps from SED modelling of the WFC3
photometry and measure their H-alpha luminosity, metallicity and outflow
properties from the OSIRIS data. With strong star formation driven outflows in
four clumps, RCSGA0327 is the first high redshift SFG at stellar mass <10^10
M_sun with spatially resolved stellar winds. We compare the H-alpha
luminosities, sizes and dispersions of the star-forming regions to other high-z
clumps as well as local giant HII regions and find no evidence for increased
clump star formation surface densities in interacting systems, unlike in the
local Universe. Spatially resolved SED modelling unveils an established stellar
population at the location of the largest clump and a second mass concentration
near the edge of the system which is not detected in H-alpha emission. This
suggests a picture of an equal-mass mixed major merger, which has not triggered
a new burst of star formation or caused a tidal tail in the gas-poor component.Comment: 22 pages, 16 figures, accepted to Ap
The determinants of savings in the third pension pillar
The paper analyses participation in and contributions to the third pillar of the pension system by Belgian households. This pillar represents individual saving for retirement and has been growing rapidly. A detailed dataset of tax declarations over the period from 1993 until 2003 was used to analyse the possible determinants of saving in the third pillar. Firstly, this dataset makes an analysis from a macroeconomic point of view possible, showing an apparent increase in total contributions to the third pillar by 39 p.c. in real terms between 1993 and 2003. This increase is mainly due to a rise in the participation rate (29 p.c. in 1993 and 40 p.c. in 2003). A detailed analysis is provided across the age groups, which further shows the influence of the demographic evolution, the average income of the participants in the third pillar and the contribution rate. The dataset also helps point up a wide number of possible microeconomic determinants of saving for retirement, such as age, income, professional status, civil status, region of residence, property ownership, employment situation, participation in second pillar pension schemes, number of dependents, etc. Moreover, the database allows a distinction to be made between the two forms in the third pillar : pension saving and life insurance. From such a microeconomic point of view, the analysis sheds some light on the major determinants of participation to the third pillar. The main findings show that older households are more likely to opt for a third pillar pension scheme. Furthermore, it appears that households consider the two forms of the third pillar as being complementary rather than substitutes for each other : households that participate in pension saving schemes are also more likely to take out life insurance and vice versa. Besides age, the other determinants that have a positive impact on participation in the third pillar of the pension system are : having higher income, being self-employed, getting an early retirement pension, being a home owner, being married and living in Flanders rather than Brussels or Wallonia.personal finance, pension fund, life insurance, private pensions
Probing Individual Star Forming Regions Within Strongly Lensed Galaxies at z > 1
Star formation occurs on physical scales corresponding to individual star
forming regions, typically of order ~100 parsecs in size, but current
observational facilities cannot resolve these scales within field galaxies
beyond the local universe. However, the magnification from strong gravitational
lensing allows us to measure the properties of these discrete star forming
regions within galaxies in the distant universe. New results from
multi-wavelength spectroscopic studies of a sample of extremely bright, highly
magnified lensed galaxies are revealing the complexity of star formation on
sub-galaxy scales during the era of peak star formation in the universe. We
find a wide range of properties in the rest-frame UV spectra of individual
galaxies, as well as in spectra that originate from different star forming
regions within the same galaxy. Large variations in the strengths and velocity
structure of Lyman-alpha and strong P Cygni lines such as C IV, and MgII
provide new insights into the astrophysical relationships between extremely
massive stars, the elemental abundances and physical properties of the nebular
gas those stars ionize, and the galactic-scale outflows they power.Comment: 4 pages, 3 figures. To be published in the Proceedings of IAU
Symposium 309. For more details and closely related work see also
arXiv:1310.6695 and arXiv:1406.335
On the lack of correlation between Mg II 2796, 2803 Angstrom and Lyman alpha emission in lensed star-forming galaxies
We examine the Mg II 2796, 2803 Angstrom, Lyman alpha, and nebular line
emission in five bright star-forming galaxies at 1.66<z<1.91 that have been
gravitationally lensed by foreground galaxy clusters. All five galaxies show
prominent Mg II emission and absorption in a P Cygni profile. We find no
correlation between the equivalent widths of Mg II and Lyman alpha emission.
The Mg II emission has a broader range of velocities than do the nebular
emission line profiles; the Mg II emission is redshifted with respect to
systemic by 100 to 200 km/s. When present, Lyman alpha is even more redshifted.
The reddest components of Mg II and Lyman alpha emission have tails to 500-600
km/s, implying a strong outflow. The lack of correlation in the Mg II and Lyman
alpha equivalent widths, the differing velocity profiles, and the high ratios
of Mg II to nebular line fluxes together suggest that the bulk of Mg II
emission does not ultimately arise as nebular line emission, but may instead be
reprocessed stellar continuum emission.Comment: The Astrophysical Journal, in press. 6 pages, 2 figure
The stellar mass structure of massive galaxies from z=0 to z=2.5; surface density profiles and half-mass radii
We present stellar mass surface density profiles of a mass-selected sample of
177 galaxies at 0.5 < z < 2.5, obtained using very deep HST optical and
near-infrared data over the GOODS-South field, including recent CANDELS data.
Accurate stellar mass surface density profiles have been measured for the first
time for a complete sample of high-redshift galaxies more massive than 10^10.7
M_sun. The key advantage of this study compared to previous work is that the
surface brightness profiles are deconvolved for PSF smoothing, allowing
accurate measurements of the structure of the galaxies. The surface brightness
profiles account for contributions from complex galaxy structures such as rings
and faint outer disks. Mass profiles are derived using radial rest-frame u-g
color profiles and a well-established empirical relation between these colors
and the stellar mass-to-light ratio. We derive stellar half-mass radii from the
mass profiles, and find that these are on average ~25% smaller than rest-frame
g band half-light radii. This average size difference of 25% is the same at all
redshifts, and does not correlate with stellar mass, specific star formation
rate, effective surface density, Sersic index, or galaxy size. Although on
average the difference between half-mass size and half-light size is modest,
for approximately 10% of massive galaxies this difference is more than a factor
two. These extreme galaxies are mostly extended, disk-like systems with large
central bulges. These results are robust, but could be impacted if the central
dust extinction becomes high. ALMA observations can be used to explore this
possibility. These results provide added support for galaxy growth scenarios
wherein massive galaxies at these epochs grow by accretion onto their outer
regions.Comment: 11 pages, 8 figures, 3 tables, accepted for publication in Ap
Spatially Resolved Galactic Wind in Lensed Galaxy RCSGA 032727-132609
We probe the spatial distribution of outflowing gas along four lines of sight
separated by up to 6 kpc in a gravitationally-lensed star-forming galaxy at
z=1.70. Using MgII and FeII emission and absorption as tracers, we find that
the clumps of star formation are driving galactic outflows with velocities of
-170 to -250 km/sec. The velocities of MgII emission are redshifted with
respect to the systemic velocities of the galaxy, consistent with being
back-scattered. By contrast, the FeII fluorescent emission lines are either
slightly blueshifted or at the systemic velocity of the galaxy. Taken together,
the velocity structure of the MgII and FeII emission is consistent with arising
through scattering in galactic winds. Assuming a thin shell geometry for the
out owing gas, the estimated masses carried out by these outfows are large (>
30 - 50 ), with mass loading factors several times the
star-formation rate. Almost 20% to 50% of the blueshifted absorption probably
escapes the gravitational potential of the galaxy. In this galaxy, the outflow
is "locally sourced", that is, the properties of the outflow in each line of
sight are dominated by the properties of the nearest clump of star formation;
the wind is not global to the galaxy. The mass outflow rates and the momentum
flux carried out by outflows in individual star forming knots of this object
are comparable to that of starburst galaxies in the local Universe.Comment: 19 pages, 10 figure, accepted for publication in MNRA
The size-star formation relation of massive galaxies at 1.5<z<2.5
We study the relation between size and star formation activity in a complete
sample of 225 massive (M > 5 x 10^10 Msun) galaxies at 1.5<z<2.5, selected from
the FIREWORKS UV-IR catalog of the CDFS. Based on stellar population synthesis
model fits to the observed restframe UV-NIR SEDs, and independent MIPS 24
micron observations, 65% of galaxies are actively forming stars, while 35% are
quiescent. Using sizes derived from 2D surface brightness profile fits to high
resolution (FWHM_{PSF}~0.45 arcsec) groundbased ISAAC data, we confirm and
improve the significance of the relation between star formation activity and
compactness found in previous studies, using a large, complete mass-limited
sample. At z~2, massive quiescent galaxies are significantly smaller than
massive star forming galaxies, and a median factor of 0.34+/-0.02 smaller than
galaxies of similar mass in the local universe. 13% of the quiescent galaxies
are unresolved in the ISAAC data, corresponding to sizes <1 kpc, more than 5
times smaller than galaxies of similar mass locally. The quiescent galaxies
span a Kormendy relation which, compared to the relation for local early types,
is shifted to smaller sizes and brighter surface brightnesses and is
incompatible with passive evolution. The progenitors of the quiescent galaxies,
were likely dominated by highly concentrated, intense nuclear star bursts at
z~3-4, in contrast to star forming galaxies at z~2 which are extended and
dominated by distributed star formation.Comment: 6 pages, 4 figures, accepted for publication in Ap
The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MEGaSaURA) I: The Sample and the Spectra
We introduce Project MEGaSaURA: The Magellan Evolution of Galaxies
Spectroscopic and Ultraviolet Reference Atlas. MEGaSaURA comprises
medium-resolution, rest-frame ultraviolet spectroscopy of N=15 bright
gravitationally lensed galaxies at redshifts of 1.68z3.6, obtained with
the MagE spectrograph on the Magellan telescopes. The spectra cover the
observed-frame wavelength range \AA ; the average
spectral resolving power is R=3300. The median spectrum has a signal-to-noise
ratio of per resolution element at 5000 \AA . As such, the MEGaSaURA
spectra have superior signal-to-noise-ratio and wavelength coverage compared to
what COS/HST provides for starburst galaxies in the local universe. This paper
describes the sample, the observations, and the data reduction. We compare the
measured redshifts for the stars, the ionized gas as traced by nebular lines,
and the neutral gas as traced by absorption lines; we find the expected bulk
outflow of the neutral gas, and no systemic offset between the redshifts
measured from nebular lines and the redshifts measured from the stellar
continuum. We provide the MEGaSaURA spectra to the astronomical community
through a data release.Comment: Resubmitted to AAS Journals. Data release will accompany journal
publication. v2 addresses minor comments from refere
Optical Spectroscopy of Distant Red Galaxies
We present optical spectroscopic follow-up of a sample of Distant Red
Galaxies (DRGs) with K 2.3, in the Hubble Deep
Field South, the MS 1054-03 field, and the Chandra Deep Field South.
Spectroscopic redshifts were obtained for 15 DRGs. Only 2 out of 15 DRGs are
located at z < 2, suggesting a high efficiency to select high-redshift sources.
From other spectroscopic surveys in the CDFS targeting intermediate to high
redshift populations selected with different criteria, we find spectroscopic
redshifts for a further 30 DRGs. We use the sample of spectroscopically
confirmed DRGs to establish the high quality (scatter in \Delta z/(1+z) of ~
0.05) of their photometric redshifts in the considered deep fields, as derived
with EAZY (Brammer et al. 2008). Combining the spectroscopic and photometric
redshifts, we find that 74% of DRGs with K 2. The combined
spectroscopic and photometric sample is used to analyze the distinct intrinsic
and observed properties of DRGs at z 2. In our photometric sample
to K < 22.5, low-redshift DRGs are brighter in K than high-redshift DRGs by 0.7
mag, and more extincted by 1.2 mag in Av. Our analysis shows that the DRG
criterion selects galaxies with different properties at different redshifts.
Such biases can be largely avoided by selecting galaxies based on their
rest-frame properties, which requires very good multi-band photometry and high
quality photometric redshifts.Comment: Accepted for publication in the Astrophysical Journal, 13 pages, 8
figures, 5 table
Stellar Populations of Highly Magnified Lensed Galaxies: Young Starbursts at z~2
We present a comprehensive analysis of the rest-frame UV to near-IR spectral
energy distributions and rest-frame optical spectra of four of the brightest
gravitationally lensed galaxies in the literature: RCSGA 032727-132609 at
z=1.70, MS1512-cB58 at z=2.73, SGAS J152745.1+065219 at z=2.76 and SGAS
J122651.3+215220 at z=2.92. This includes new Spitzer imaging for RCSGA0327 as
well as new spectra, near-IR imaging and Spitzer imaging for SGAS1527 and
SGAS1226. Lensing magnifications of 3-4 magnitudes allow a detailed study of
the stellar populations and physical conditions. We compare star formation
rates as measured from the SED fit, the H-alpha and [OII] emission lines, and
the UV+IR bolometric luminosity where 24 micron photometry is available. The
SFR estimate from the SED fit is consistently higher than the other indicators,
which suggests that the Calzetti dust extinction law used in the SED fitting is
too flat for young star-forming galaxies at z~2. Our analysis finds similar
stellar population parameters for all four lensed galaxies: stellar masses
3-7*10^9 M_sun, young ages ~ 100 Myr, little dust content E(B-V)=0.10-0.25, and
star formation rates around 20-100 M_sun/yr. Compared to typical values for the
galaxy population at z~2, this suggests we are looking at newly formed,
starbursting systems that have only recently started the build-up of stellar
mass. These results constitute the first detailed, uniform analysis of a sample
of the growing number of strongly lensed galaxies known at z~2.Comment: 13 pages, 8 figures, Accepted to Ap
- …