European Southern Observatory

About: European Southern Observatory is a facility organization based out in Garching bei München, Germany. It is known for research contribution in the topics: Galaxy & Stars. The organization has 3594 authors who have published 16157 publications receiving 823095 citations. The organization is also known as: The European Southern Observatory，ESO & ESO.

THE NUMBER DENSITY AND MASS DENSITY OF STAR-FORMING AND QUIESCENT GALAXIES AT 0.4 ⩽ z ⩽ 2.2

Abstract: We study the buildup of the bimodal galaxy population using the NEWFIRM Medium-Band Survey, which provides excellent redshifts and well-sampled spectral energy distributions of {approx}27, 000 galaxies with K 3 x 10{sup 10} M{sub sun} increases by a factor of {approx}10 from z {approx} 2 to the present day, whereas the mass density in star-forming galaxies is flat or decreases over the same time period. Modest mass growth by a factor of {approx}2 of individual quiescent galaxies can explain roughly half of the strong density evolution at masses >10{sup 11} M{sub sun}, due to the steepness of the exponential tail of the mass function. The rest of the density evolution of massive, quiescent galaxies is likely due to transformation (e.g., quenching) of the massive star-forming population, a conclusion which ismore » consistent with the density evolution we observe for the star-forming galaxies themselves, which is flat or decreasing with cosmic time. Modest mass growth does not explain the evolution of less massive quiescent galaxies ({approx}10{sup 10.5} M{sub sun}), which show a similarly steep increase in their number densities. The less massive quiescent galaxies are therefore continuously formed by transforming galaxies from the star-forming population.« less

IRAC Mid-Infrared Imaging of the Hubble Deep Field-South: Star Formation Histories and Stellar Masses of Red Galaxies at z > 2*

Abstract: We present deep 3.6–8 mm imaging of the Hubble Deep Field–South with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We study distant red galaxies (DRGs) at z 1 2 selected by JsKs 1 2.3 and compare them with a sample of Lyman break galaxies (LBGs) at z p 2–3. The observed UV–to–8 mm spectral energy distributions are fitted with stellar population models to constrain star formation histories and derive stellar masses. We find that 70% of the DRGs are best described by dust-reddened star-forming models and 30% are very well fitted with old and “dead” models. Using only the IKs and Ks4.5 mm colors, we can effectively separate the two groups. The dead systems are among the most massive at z ∼ 2.5 (mean stellar mass AM * S p 0.8 #10 11 M,) and likely formed most of their stellar mass at z 1 5. To a limit of 0.5 #10 11 M,, their number density is ∼10 times lower than that of local early-type galaxies. Furthermore, we use the IRAC photometry to derive rest-frame near-infrared J, H, and K fluxes. The DRGs and LBGs together show a large variation (a factor of 6) in the rest-frame K-band mass-to-light ratios (M/LK), implying that even a Spitzer 8 mm–selected sample would be very different from a mass-selected sample. The average M/LK of the DRGs is about 3 times higher than that of the LBGs, and DRGs dominate the high-mass end. The M/LK values and ages of the two samples appear to correlate with derived stellar mass, with the most massive galaxies being the oldest and having the highest mass-to-light ratios, similar to what is found in the low-redshift universe. Subject headings: galaxies: evolution — galaxies: high-redshift — infrared: galaxies

A Fundamental Relation between Compact Stellar Nuclei, Supermassive Black Holes, and Their Host Galaxies

Abstract: Imaging surveys with the Hubble Space Telescope (HST) have shown that ?50%-80% of low- and intermediate-luminosity galaxies contain a compact stellar nucleus at their center, regardless of host galaxy morphological type. We combine HST imaging for early-type galaxies from the ACS Virgo Cluster Survey with ground-based long-slit spectra from KPNO to show that the masses of compact stellar nuclei in Virgo Cluster galaxies obey a tight correlation with the masses of the host galaxies. The same correlation is obeyed by the supermassive black holes (SBHs) found in predominantly massive galaxies. The compact stellar nuclei in the Local Group galaxies M33 and NGC 205 are also found to fall along this same scaling relation. These results indicate that a generic by-product of galaxy formation is the creation of a central massive object (CMO)?either an SBH or a compact stellar nucleus?that contains a mean fraction, ?0.2%, of the total galactic mass. In galaxies with masses greater than gal ~ a few × 1010 ?, SBHs appear to be the dominant mode of CMO formation.

The Deuterium Abundance toward Q1937–1009

Abstract: We present a new measurement of the deuterium-to-hydrogen ratio (D/H) in the Lyman limit absorption system at z = 3.572 toward Q1937-1009. Tytler, Fan & Burles (TFB) made the first extragalactic detection of deuterium in this absorption system, which remains the best location for a high-accuracy measurement of primordial D/H. Their detailed analysis of Keck spectra gave a low value of D/H = 2.3 ± 0.3 ± 0.3 × 10-5 (1 σ statistical and systematic errors). Now we present a new method to measure D/H in QSO absorption systems. We avoid many of the assumptions adopted by TFB; we allow extra parameters to treat the continuum uncertainties, include a variety of new absorption models that allow for undetected velocity structure, and use the improved measurement of the total hydrogen column density by Burles & Tytler. We find that all models, including contamination, give an upper limit of D/H < 3.9 × 10-5 (95% confidence). Both this and previous analyses find contamination to be unlikely in this absorption system: a χ2 analysis in models without contamination gives D/H = 3.3 ± 0.3 × 10-5 (67% confidence), which is higher but consistent with the earlier results of TFB, and a second measurement of D/H toward Q1009+2956. With calculations of standard big bang nucleosynthesis (SBBN) and the assumption that this measurement of D/H is representative of the primordial value, we find a high baryon-to-photon ratio, η = 5.3 ± 0.4 × 10-10. This is consistent with primordial abundance determinations of 4He in H II regions and 7Li in the atmospheres of warm metal-poor Population II stars. We find a high value for the present-day baryon density, Ωbh2 = 0.0193 ± 0.0014, which is consistent with other inventories of baryonic matter, from low to high redshift: clusters of galaxies, the Lyman alpha forest & the cosmic microwave background.

A giant outburst two years before the core-collapse of a massive star

Abstract: The death of massive stars produces a variety of supernovae, which are linked to the structure of the exploding stars. The detection of several precursor stars of type II supernovae has been reported (see, for example, ref. 3), but we do not yet have direct information on the progenitors of the hydrogen-deficient type Ib and Ic supernovae. Here we report that the peculiar type Ib supernova SN 2006jc is spatially coincident with a bright optical transient that occurred in 2004. Spectroscopic and photometric monitoring of the supernova leads us to suggest that the progenitor was a carbon-oxygen Wolf-Rayet star embedded within a helium-rich circumstellar medium. There are different possible explanations for this pre-explosion transient. It appears similar to the giant outbursts of luminous blue variable stars (LBVs) of 60-100 solar masses, but the progenitor of SN 2006jc was helium- and hydrogen-deficient (unlike LBVs). An LBV-like outburst of a Wolf-Rayet star could be invoked, but this would be the first observational evidence of such a phenomenon. Alternatively, a massive binary system composed of an LBV that erupted in 2004, and a Wolf-Rayet star exploding as SN 2006jc, could explain the observations.