318 research outputs found
The Physical Properties of LBGs at z>5: Outflows and the "pre-enrichment problem"
We discuss the properties of Lyman Break galaxies (LBGs) at z>5 as determined
from disparate fields covering approximately 500 sq. arcmin. While the broad
characteristics of the LBG population has been discussed extensively in the
literature, such as luminosity functions and clustering amplitude, we focus on
the detailed physical properties of the sources in this large survey (>100 with
spectroscopic redshifts). Specifically, we discuss ensemble mass estimates,
stellar mass surface densities, core phase space densities, star-formation
intensities, characteristics of their stellar populations, etc as obtained from
multi-wavelength data (rest-frame UV through optical) for a subsample of these
galaxies. In particular, we focus on evidence that these galaxies drive
vigorous outflows and speculate that this population may solve the so-called
``pre-enrichment problem''. The general picture that emerges from these studies
is that these galaxies, observed about 1 Gyr after the Big Bang, have
properties consistent with being the progenitors of the densest stellar systems
in the local Universe -- the centers of old bulges and early type galaxies.Comment: 4 pages, to appear in "Pathways Through an Eclectic Universe", J. H.
Knappen, T. J. Mahoney, and A. Vazedekis (Eds.), ASP Conf. Ser., 200
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
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
Spectroscopic Confirmation of Multiple Red Galaxy-Galaxy Mergers in MS1054-03 (z=0.83)
We present follow-up spectroscopy of the galaxy cluster MS1054-03 (z=0.83)
confirming that at least six of the nine merging galaxy pairs identified by van
Dokkum et al. (1999) are indeed bound systems: they have projected separations
of R_s<10 kpc and relative line-of sight velocities of dv<165 km/s. For the
remaining three pairs, we were unable to obtain redshifts of both constituent
galaxies. To identify a more objective sample of merging systems, we select
bound red galaxy pairs (R_s<=30 kpc, dv<=300 km/s) from our sample of 121
confirmed cluster members: galaxies in bound red pairs make up 15.7+/-3.6% of
the cluster population. The (B-K_s) color-magnitude diagram shows that the pair
galaxies are as red as the E/S0 members and have a homogeneous stellar
population. The red pair galaxies span a large range in luminosity and internal
velocity dispersion to include some of the brightest, most massive members
(L>L*, sigma>200 km/s); these bound galaxy pairs must evolve into E/S0 members
by z~0.7. These results combined with MS1054's high merger fraction and
reservoir of likely future mergers indicates that most, if not all, of its
early-type members evolved from (passive) galaxy-galaxy mergers at z<~1.Comment: accepted by ApJ Letters; high resolution version of Fig. 2 available
at http://www.exp-astro.phys.ethz.ch/tran/outgoing/ms1054mgrs.ps.g
FIREWORKS U38-to-24 micron photometry of the GOODS-CDFS: multi-wavelength catalog and total IR properties of distant Ks-selected galaxies
We present a Ks-selected catalog, dubbed FIREWORKS, for the Chandra Deep
Field South (CDFS) containing photometry in U_38, B_435, B, V, V_606, R, i_775,
I, z_850, J, H, Ks, [3.6 um], [4.5 um], [5.8 um], [8.0 um], and the MIPS [24
um] band. The imaging has a typical Ks limit of 24.3 mag (5 sigma, AB) and
coverage over 113 arcmin^2 in all bands and 138 arcmin^2 in all bands but H. We
cross-correlate our catalog with the 1 Ms X-ray catalog by Giacconi et al.
(2002) and with all available spectroscopic redshifts to date. We find and
explain systematic differences in a comparison with the 'z_850 + Ks'-selected
GOODS-MUSIC catalog that covers ~90% of the field. We exploit the U38-to-24
micron photometry to determine which Ks-selected galaxies at 1.5<z<2.5 have the
brightest total IR luminosities and which galaxies contribute most to the
integrated total IR emission. The answer to both questions is that red galaxies
are dominating in the IR. This is true no matter whether color is defined in
the rest-frame UV, optical, or optical-to-NIR. We do find however that among
the reddest galaxies in the rest-frame optical, there is a population of
sources with only little mid-IR emission, suggesting a quiescent nature.Comment: Accepted for publication in the Astrophysical Journal, 20 pages, 10
figures, reference to website correcte
Deep VLT V-band Imaging of the Field of a z=10 Candidate Galaxy: Below the Lyman Limit?
We present a deep 16.8 ks V-band image of the field of a candidate z=10
galaxy magnified by the foreground (z=0.25) cluster A1835. The image was
obtained with FORS1 on VLT-Kueyen to test whether the V-band lies below the
Lyman limit for this very high redshift candidate. A detection would
unambiguously rule out that the source is at z=10. The 3sigma detection limit
of the image in the area of the z=10 candidate is V_AB=28.0 mag in a 2 arcsec
diameter aperture (about 3 times the seeing FWHM of 0.7 arcsec). No source at
the position of the candidate galaxy is detected down to this limit. Formally,
this is consistent with the V-band probing below the Lyman limit in the
rest-frame of a z=10 source. However, given the recent non-detection of the
object in a deep H-band exposure with NIRI on Gemini North down to H_AB=26.0
mag (3sigma in a 1.4 arcsec aperture) and concerns about the detection of the
reported associated emission line, it may be possible that this source is
spurious. We discuss several astrophysical possibilities to explain the
puzzling nature of this source and find none of them compelling.Comment: accepted for publication in Ap
An Arc of Young Stars in the Halo of M82
The properties of the brightest resolved stars in an arc that was originally
identified by Sun et al. (2005) and is located in the extraplanar regions of
M82 are discussed. The stars form an elongated structure that is traced over a
projected area of 3.0 x 0.8 kpc. The integrated brightness is M_V ~ -11, while
the total stellar mass is between 3 x 10^5 and 2 x 10^6 solar masses. If there
is only foreground extinction then the youngest stars have a metallicity Z >
0.008 and an age log(tyears) ~ 7.75; thus, the youngest stars formed at roughly
the same time as stars in tidal features that are associated with other M81
Group galaxies. If the arc is dispersing then it will deposit young, chemically
enriched stars into the M82 halo.Comment: 11 pages including 3 postscript figures; accepted for publication in
ApJ (Letters
Archäologie als Empowerment: Für wen und wie? Kommentare zu wissenschaftlichem Aktivismus
On the occasion of the 10th anniversary of Forum Kritische Archäologie, the editorial collective reflected on what has been achieved and what we originally imagined for this journal. While we think that the number of contributions with a critical edge that have been published in our journal over the last 10 years is encouraging, and in many ways innovative, there is still a lot to do in one respect: to advance critical discussions in German archaeology itself. German scholarship continues to construct its discourses largely along the line of cultural-historical knowledge, and university teaching is only slowly integrating theoretical or critical perspectives. So we pondered the question of how the development of more critical approaches in German-speaking archaeology could be supported. We decided to ask authors – international and German – to write about political issues, specifically an activist archaeology. The following set of papers is conceptually similar to those in the first volume of our journal, Forum Kritische Archäologie Special Issue: What is a Critical Archaeology? This time, too, we sent authors a set of questions that we asked them to reflect upon in short essays.Anlässlich des 10-jährigen Bestehens des Forum Kritische Archäologie im Jahr 2022 haben wir im Herausgeber* innenkollektiv darüber nachgedacht, was mit dem Forum bisher erreicht wurde und was wir uns ursprünglich für diese Zeitschrift vorgestellt hatten. Während wir die Anzahl der kritischen Beiträge, die in den letzten 10 Jahren in unserer Zeitschrift veröffentlicht wurden, für ermutigend und in vielerlei Hinsicht innovativ halten, haben wir das Gefühl, dass es in einer Hinsicht noch viel zu tun gibt: die kritische Diskussion in der deutschen Archäologie selbst voranzutreiben. Die deutsche Wissenschaft entwickelt ihre Diskurse nach wie vor weitgehend im Rahmen kulturhistorischer Denkansätze, und die universitäre Lehre integriert nur langsam theoretisch fundierte oder kritischere Perspektiven. Wir haben uns daher gefragt, wie die Entwicklung solcher Ansätze in der deutschsprachigen Archäologie unterstützt werden kann, und uns entschieden, Kolleg*innen – internationale wie deutsche – zu bitten, über politische Formen der Archäologie zu schreiben, insbesondere über solche die als aktivistisch verstanden werden können. Die folgenden Beiträge ähneln konzeptionell denen im ersten Band unserer Zeitschrift (Forum Kritische Archäologie 1/Themenheft: Was ist eine kritische Archäologie?). Auch dieses Mal haben wir den Autor*innen eine Reihe von Fragen gestellt und sie gebeten, diese in kurzen Essays zu reflektieren
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