71 research outputs found
Bulge-to-disk decomposition of large galaxies in the Sloan Digital Sky Survey
Die moderne Astrophysik steht vor der Herausforderung, neueste
Beobachtungen mit den theoretischen und numerischen Modellen der
Galaxienentstehung und -entwicklung zu konfrontieren. So hofft man, die
wichtigsten physikalischen Prozesse und ihre Zeitskalen identifizieren zu
koennen.
In dieser Arbeit nehmen wir eine komplette, helligkeits--limitierte Auswahl
von 1862 Galaxien aus der Sloan Digital Sky Survey (SDSS), um eine Anzahl
von globalen und strukturellen Parametern zu untersuchen. Diese Auswahl
beinhaltet helle Objekte mit einer r--Band Helligkeit von < 15.9 im nahen
Universum mit einer Rotverschiebung von z < 0.12. Sie enthaelt
elliptische, Spiral- und irregulaere Galaxien. Photometrische Daten sind
fuer die u, g, r, i und z--Baender angegeben und von 1588 Galaxien
wurden
nachtraeglich Spektra genommen. Die `Bulge' Komponente der Galaxien
wird mit Sersic und de Vaucouleurs Modellen modelliert, waehrend die
Scheibenkomponente mit einer exponentiellen Verteilung modelliert wird.
Die Messung des Lichtanteils in `Bulge' und Scheibenkomponente gibt
Aufschluss ueber die Effizienz des hierarchischen
Strukturbildungsprozesses.
In Kapitel 3 zeigen wir, dass der mittlere Anteil des
Lichts aus der
Scheibe stark mit der totalen absoluten Helligkeit der Galaxie zunimmt.
Unabhaengige r und i Band Analysen ergeben einen sehr aehnlichen Trend.
Zum ersten Mal schaetzen wir den volumengemittelten Anteil des Lichts aus
der Scheibenkomponente von Galaxien ab und stellen fest, dass ungefaehr
(55 +- 2) % des gesamten Lichts im lokalen Universum aus Scheiben kommt.
Wir ermitteln auch die Leuchtkraftfunktion fuer reine 'Bulges', also fuer
Strukturen ohne Scheibenanteil, die nicht einfache Spheroide sind.
In Kapitel 4 studieren wir die Abhaengigkeiten von visuellen und
quantitativen morphologischen Klassifikationskriterien mit dem Ziel
sauberere Galaxienkataloge zu erstellen, besonders bei hohen
Rotverschiebungen, wo die Klassifikation schwierig ist. Wir finden, dass
Galaxienfarben, effektive Oberflaechenhelligkeit, Masse/Licht Anteil, und
Asymmetrie Parameter einen Mehrparameter Raum aufspannen, in der alle
Galaxien je nach morphologischem Typ eindeutig positioniert sind.
In Kapitel 5 beobachten wir einen klaren Trend, mit dem die Skalenlaenge
der Scheiben mit ihrer Helligkeit zunimmt, und dieser Trend ist
unabhaengig vom photometrischen Band und der morphologischen Klasse. Es
existiert auch eine klare Abhaengigkeit zwischen dem effektiven Radius des
`Bulge' und seiner Helligkeit, aber die Steigung dieser Relation aendert
sich mit dem morphologischem Typ. Sie ist steiler fuer fruehere Typus, was
uns zu der Schlussfolgerung fuehrt, dass die Skalenlaenge weniger von der
Morphologie abhaengt als die Skalenlaenge des `Bulges'. Dies legt nahe,
dass `Bulges' in fruehen und spaeteren Galaxien in unterschiedlichen
Prozessen gebildet werden. Wir finden auch eine Korrelation zwischen den
strukturellen Parametern von Scheiben und `Bulges', insbesondere zwischen
effektivem Radius der `Bulges' und der Skalenlaenge der Scheiben in
Systemen fruehen Typus. Wir interpretieren dies als Beweisstueck
zugunsten von saekularen Evolutionsmodellen
The Dominant Role of Mergers in the Size Evolution of Massive Galaxies since z∼1
We estimate the merger rate, both major (stellar mass ratio μ = M★,_2/M★,_1 ≥ 1/4) and minor (1/10 ≤ μ < 1/4), of massive (M★ ≥ 10^(11) M☉) early-type galaxies (ETGs) in the COSMOS field by close pairs statistics. The merger rate of massive ETGs evolves as a power-law (1+z)^n, showing the minor merger little evolution with redshift, n_(mm) ∼ 0, in contrast with the increase of major mergers, n_(MM) = 1.8. Our results shows that massive ETGs have undergone 0.89 mergers (0.43 major and 0.46 minor) since z ∼ 1, leading to a mass growth of ∼ 30%. In addition, μ ≥ 1/10 mergers can explain ∼ 55% of the observed size evolution of these galaxies since z ∼ 1. Another ∼ 20% is due to the progenitor bias (younger galaxies are more extended) and we estimate that very minor mergers (μ < 1/10) could contribute with an extra ∼ 20%. The remaining ∼ 5% should come from other processes (e.g., adiabatic expansion or observational effects). These results suggest that mergers are the main contributor to the size evolution of massive ETGs, accounting for ∼ 55%–75% of that evolution in the last 8 Gyr. Nearly half of this merging evolution is related with minor (μ < 1/4) events
Pixel-z: Studying Substructure and Stellar Populations in Galaxies out to z~3 using Pixel Colors I. Systematics
We perform a pixel-by-pixel analysis of 467 galaxies in the GOODS-VIMOS
survey to study systematic effects in extracting properties of stellar
populations (age, dust, metallicity and SFR) from pixel colors using the
pixel-z method. The systematics studied include the effect of the input stellar
population synthesis model, passband limitations and differences between
individual SED fits to pixels and global SED-fitting to a galaxy's colors. We
find that with optical-only colors, the systematic errors due to differences
among the models are well constrained. The largest impact on the age and SFR
e-folding time estimates in the pixels arises from differences between the
Maraston models and the Bruzual&Charlot models, when optical colors are used.
This results in systematic differences larger than the 2{\sigma} uncertainties
in over 10 percent of all pixels in the galaxy sample. The effect of
restricting the available passbands is more severe. In 26 percent of pixels in
the full sample, passband limitations result in systematic biases in the age
estimates which are larger than the 2{\sigma} uncertainties. Systematic effects
from model differences are reexamined using Near-IR colors for a subsample of
46 galaxies in the GOODS-NICMOS survey. For z > 1, the observed optical/NIR
colors span the rest frame UV-optical SED, and the use of different models does
not significantly bias the estimates of the stellar population parameters
compared to using optical-only colors. We then illustrate how pixel-z can be
applied robustly to make detailed studies of substructure in high redshift
galaxies such as (a) radial gradients of age, SFR, sSFR and dust and (b) the
distribution of these properties within subcomponents such as spiral arms and
clumps. Finally, we show preliminary results from the CANDELS survey
illustrating how the new HST/WFC3 data can be exploited to probe substructure
in z~1-3 galaxies.Comment: 37 pages, 21 figures, submitted to Ap
The EFIGI catalogue of 4458 nearby galaxies with detailed morphology
Accepted for publication in Astronomy and Astrophysics, 27 pages, 7 tables, 32 colour figures. Data available at http://www.efigi.orgInternational audienceNow that large databases of resolved galaxy images are provided by modern imaging surveys, advanced morphological studies can be envisioned, urging for well defined calibration samples. We present the EFIGI catalogue, a multiwavelength database specifically designed for a dense sampling of all Hubble types. The catalogue merges data from standard surveys and catalogues (Principal Galaxy Catalogue, Sloan Digital Sky Survey, Value-Added Galaxy Catalogue, HyperLeda, and the NASA Extragalactic Database) and provides detailed morphological information. Imaging data are obtained from the SDSS DR4 in the u, g, r, i, and z bands for a sample of 4458 PGC galaxies, whereas photometric and spectroscopic data are obtained from the SDSS DR5 catalogue. Point-Spread Function models are derived in all five bands. Composite colour images of all objects are visually examined by a group of astronomers, and galaxies are staged along the Hubble sequence and classified according to 16 morphological attributes describing their structure, texture, as well as environment and appearance on a five-level scale. The EFIGI Hubble sequence shows remarkable agreement with the RC3 Revised Hubble Sequence. The main characteristics and reliability of the catalogue are examined, including photometric completeness, type mix, systematic trends and correlations. The final EFIGI database is a large sub-sample of the local Universe, with a dense sampling of Sd, Sdm, Sm and Im types compared to magnitude-limited catalogues. We estimate the photometric catalogue to be more than ~ 80% complete for galaxies with 10 < g < 14. More than 99.5% of EFIGI galaxies have a known redshift in the HyperLeda and NED databases
ALMA reveals the molecular gas properties of five star-forming galaxies across the main sequence at 3
International audienceWe present the detection of CO(5-4) with S/N> 7 - 13 and a lower CO transition with S/N > 3 (CO(4-3) for 4 galaxies, and CO(3-2) for one) with ALMA in band 3 and 4 in five main sequence star-forming galaxies with stellar masses 3-6x10^10 M/M_sun at 3 < z < 3.5. We find a good correlation between the total far-infrared luminosity LFIR and the luminosity of the CO(5-4) transition L'CO(5-4), where L'CO(5-4) increases with SFR, indicating that CO(5-4) is a good tracer of the obscured SFR in these galaxies. The two galaxies that lie closer to the star-forming main sequence have CO SLED slopes that are comparable to other star-forming populations, such as local SMGs and BzK star-forming galaxies; the three objects with higher specific star formation rates (sSFR) have far steeper CO SLEDs, which possibly indicates a more concentrated episode of star formation. By exploiting the CO SLED slopes to extrapolate the luminosity of the CO(1-0) transition, and using a classical conversion factor for main sequence galaxies of alpha_CO = 3.8 M_sun(K km s^-1 pc^-2)^-1, we find that these galaxies are very gas rich, with molecular gas fractions between 60 and 80%, and quite long depletion times, between 0.2 and 1 Gyr. Finally, we obtain dynamical masses that are comparable with the sum of stellar and gas mass (at least for four out of five galaxies), allowing us to put a first constraint on the alpha_CO parameter for main sequence galaxies at an unprecedented redshift
Discovery of Massive, Mostly Star-formation Quenched Galaxies with Extremely Large Lyman-alpha Equivalent Widths at z ~ 3
We report a discovery of 6 massive galaxies with both extremely large Lya
equivalent width and evolved stellar population at z ~ 3. These MAssive
Extremely STrong Lya emitting Objects (MAESTLOs) have been discovered in our
large-volume systematic survey for strong Lya emitters (LAEs) with twelve
optical intermediate-band data taken with Subaru/Suprime-Cam in the COSMOS
field. Based on the SED fitting analysis for these LAEs, it is found that these
MAESTLOs have (1) large rest-frame equivalent width of EW_0(Lya) ~ 100--300 A,
(2) M_star ~ 10^10.5--10^11.1 M_sun, and (3) relatively low specific star
formation rates of SFR/M_star ~ 0.03--1 Gyr^-1. Three of the 6 MAESTLOs have
extended Ly emission with a radius of several kpc although they show
very compact morphology in the HST/ACS images, which correspond to the
rest-frame UV continuum. Since the MAESTLOs do not show any evidence for AGNs,
the observed extended Lya emission is likely to be caused by star formation
process including the superwind activity. We suggest that this new class of
LAEs, MAESTLOs, provides a missing link from star-forming to passively evolving
galaxies at the peak era of the cosmic star-formation history.Comment: Accepted for publication in ApJ Letters on 15th July, 2015. 6 pages
including 3 figures and 2 table
An ALMA survey of submillimetre galaxies in the COSMOS field: The extent of the radio-emitting region revealed by 3 GHz imaging with the Very Large Array
We determine the radio size distribution of a large sample of 152 SMGs in
COSMOS that were detected with ALMA at 1.3 mm. For this purpose, we used the
observations taken by the VLA-COSMOS 3 GHz Large Project. One hundred and
fifteen of the 152 target SMGs were found to have a 3 GHz counterpart. The
median value of the major axis FWHM at 3 GHz is derived to be kpc.
The radio sizes show no evolutionary trend with redshift, or difference between
different galaxy morphologies. We also derived the spectral indices between 1.4
and 3 GHz, and 3 GHz brightness temperatures for the sources, and the median
values were found to be and K. Three of the
target SMGs, which are also detected with the VLBA, show clearly higher
brightness temperatures than the typical values. Although the observed radio
emission appears to be predominantly powered by star formation and supernova
activity, our results provide a strong indication of the presence of an AGN in
the VLBA and X-ray-detected SMG AzTEC/C61. The median radio-emitting size we
have derived is 1.5-3 times larger than the typical FIR dust-emitting sizes of
SMGs, but similar to that of the SMGs' molecular gas component traced through
mid- line emission of CO. The physical conditions of SMGs probably render
the diffusion of cosmic-ray electrons inefficient, and hence an unlikely
process to lead to the observed extended radio sizes. Instead, our results
point towards a scenario where SMGs are driven by galaxy interactions and
mergers. Besides triggering vigorous starbursts, galaxy collisions can also
pull out the magnetised fluids from the interacting disks, and give rise to a
taffy-like synchrotron-emitting bridge. This provides an explanation for the
spatially extended radio emission of SMGs, and can also cause a deviation from
the well-known IR-radio correlation.Comment: 32 pages (incl. 5 appendices), 17 figures, 7 tables; accepted for
publication in A&A; abstract abridged for arXi
The zCOSMOS 10k-Bright Spectroscopic Sample
We present spectroscopic redshifts of a large sample of galaxies with I_(AB) < 22.5 in the COSMOS field, measured from spectra of 10,644 objects that have been obtained in the first two years of observations in the zCOSMOS-bright redshift survey. These include a statistically complete subset of 10,109 objects. The average accuracy of individual redshifts is 110 km s^(–1), independent of redshift. The reliability of individual redshifts is described by a Confidence Class that has been empirically calibrated through repeat spectroscopic observations of over 600 galaxies. There is very good agreement between spectroscopic and photometric redshifts for the most secure Confidence Classes. For the less secure Confidence Classes, there is a good correspondence between the fraction of objects with a consistent photometric redshift and the spectroscopic repeatability, suggesting that the photometric redshifts can be used to indicate which of the less secure spectroscopic redshifts are likely right and which are probably wrong, and to give an indication of the nature of objects for which we failed to determine a redshift. Using this approach, we can construct a spectroscopic sample that is 99% reliable and which is 88% complete in the sample as a whole, and 95% complete in the redshift range 0.5 < z < 0.8. The luminosity and mass completeness levels of the zCOSMOS-bright sample of galaxies is also discussed
Lyman-alpha Forest Tomography from Background Galaxies: The First Megaparsec-Resolution Large-Scale Structure Map at z>2
We present the first observations of foreground Lyman- forest
absorption from high-redshift galaxies, targeting 24 star-forming galaxies
(SFGs) with within a region of the COSMOS
field. The transverse sightline separation is
comoving, allowing us to create a tomographic reconstruction of the 3D
Ly forest absorption field over the redshift range . The resulting map covers in the transverse plane and
along the line-of-sight with a spatial resolution of , and is the first high-fidelity map of large-scale
structure on scales at . Our map reveals significant
structures with extent, including several
spanning the entire transverse breadth, providing qualitative evidence for the
filamentary structures predicted to exist in the high-redshift cosmic web.
Simulated reconstructions with the same sightline sampling, spectral
resolution, and signal-to-noise ratio recover the salient structures present in
the underlying 3D absorption fields. Using data from other surveys, we
identified 18 galaxies with known redshifts coeval with our map volume enabling
a direct comparison to our tomographic map. This shows that galaxies
preferentially occupy high-density regions, in qualitative agreement with the
same comparison applied to simulations. Our results establishes the feasibility
of the CLAMATO survey, which aims to obtain Ly forest spectra for SFGs over of the COSMOS field, in order to map
out IGM large-scale structure at over a large
volume .Comment: Accepted for publication in Astrophysical Journal Letters; 8 pages
and 5 figure
Weak Gravitational Lensing with COSMOS: Galaxy Selection and Shape Measurements
With a primary goal of conducting precision weak-lensing measurements from space, the COSMOS survey has imaged the largest contiguous area observed by Hubble Space Telescope to date, using the Advanced Camera for Surveys (ACS). This is the first paper in a series in which we describe our strategy for addressing the various technical challenges in the production of weak-lensing measurements from COSMOS data. We first construct a source catalog from 575 ACS/WFC tiles (1.64 deg^2) subsampled at a pixel scale of 0.03". Defects and diffraction spikes are carefully removed, leaving a total of 1.2 × 10^6 objects to a limiting magnitude of F814W = 26.5. This catalog is made publicly available. Multiwavelength follow-up observations of the COSMOS field provide photometric redshifts for 73% of the source galaxies in the lensing catalog. We analyze and discuss the COSMOS redshift distribution and show broad agreement with other surveys to z ~ 1. Our next step is to measure the shapes of galaxies and correct them for the distortion induced by the time-varying ACS point-spread function and for charge transfer efficiency (CTE) effects. Simulated images are used to derive the shear susceptibility factors that are necessary in transforming shape measurements into unbiased shear estimators. For every galaxy we derive a shape measurement error and utilize this quantity to extract the intrinsic shape noise of the galaxy sample. Interestingly, our results indicate that intrinsic shape noise varies little with size, magnitude, or redshift. Representing a number density of 66 galaxies per arcmin^2, the final COSMOS weak-lensing catalog contains 3.9 × 10^5 galaxies with accurate shape measurements. The properties of the COSMOS weak-lensing catalog described throughout this paper will provide key input numbers for the preparation and design of next-generation wide field space missions
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