Day 977

Tuesday.


Astrosat Launches
It will observed the universe n the optical, UV, low and high energy X-ray regions of the EM spectrum.  The 5 payloads of Astrosat will study star birth regions and black holes.


1509.07863
Abiotic O$_{2}$ levels on planets around F, G, K, and M stars: possible false positives for life?
Harman et al

Of the countless number of chemical species terrestrial life produces, only a few have the distinct spectral features and the necessary atmospheric abundance to be detectable.  The easiest of these species to observe in Earth's atmosphere is O2 (and its photochemical byproduct, O3).  But O2 can also be produced abiotically by photolysis of CO2, followed by recombination of O atoms with each other.  CO is produced in stoichiometric proportions.  Whether O2 and CO can accumulate to appreciable concentrations depends on the ratio of far-UV to near-UV radiation coming from the planet's parent star and on what happens to these gases when they dissolve in a planet's oceans.  Using a 1-D photochemical model, demonstrate that O2 derived from CO2 photolysis should not accumulate to measurable concentrations on planets around F- and G-type stars.  K-star, and especially M-star planets, however, may build up O2 because of the low near-UV flux from their parent stars, in agreement with some previous studies.  On such planets, a 'false positive' for life is possible if recombination of dissolved CO and O2 in the oceans is slow and if other O2 sinks (e.g., reduced volcanic gases or dissolved ferrous iron) are small.  O3, on the other hand, could be detectable at UV wavelengths (lambda<300nm) for a much broader range of boundary conditions and stellar types.


1509.07870
The galaxy luminosity function in groups and clusters: the faint-end upturn and the connection to the field luminosity function
Lan, Ménard, Mo

Characterize the LF of galaxies residing in z~0 groups and clusters over the broadest ranges of luminosity and mass reachable by SDSS.  The measurements cover 4 orders of magnitude in luminosity, down to about Mr=-12 mag or L=1e7Lsun, and 3 orders of magnitude in halo mass, from 1e12 to 1e15 Msun.  Find a characteristic scale, Mr~-18mag or L~1e9Lsun, below which the slope of the LF becomes systematically steeper.  This trend is present for all halo masses and originates mostly from red satellite galaxies.  The ubiquitous presence of this faint-end upturn suggests that it is formation, rather than halo-specific environmental effect, that plays a major role in regulating the stellar masses of faint satellites.  Show that the observed LFs of satellite galaxies can be described in a simple manner by a double Schechter function with amplitudes scaling with halo mass over the entire range of observables.  Combining these conditional LFs with the DM halo MF, can accurately recover the entire field LF measured over 10 visual magnets.  This decomposition reveals that the field LF is dominated by satellite galaxies at magnitudes fainter than -18 mag or L<1e9 Lsun and central galaxies above.  Find that the LFs of blue and red satellite galaxies show distinct shapes and present estimates of the stellar MF as a function of halo mass and galaxy type.  Finally, using a simple model, show that the average number and the faint-end slopes of blue and red satellite galaxies can be interpreted in terms of their formation history, with 2 distinct modes separated by some characteristic time.


1509.07917
The SDSS-III BOSS quasar lens survey: discovery of thirteen gravitationally lensed quasars
More, Oguri, Kayo, et al

Report the discovery of 13 confirmed 2 image quasar lenses from a systematic search for gravitationally lensed quasars in SDSS-III BOSS.  Adopted a methodology similar to SQLS (SDSS Quasar Lens  Search).  In addition to the confirmed lenses, report 11 quasar pairs with small angular separations (<~2") confirmed from spectroscopy, which are either projected pairs, physical binaries, or possibly quasar lens systems whose lens galaxies have not yet been detected.  The newly discovered quasar lens system, SDSS J1452+4224 at zs~4.8 is the one of the highest z multiply imaged quasars found to date.  Furthermore, there are over 50 good lens candidates yet to be followed up.  Owing to the heterogenous selection of BOSS quasars, the lens sample presented here does not have a well-defined selection function.


1509.08046
Quiescent luminous red galaxies (LRGs) as cocsmic chronometers: on the significance of the mass and environmental dependence
Liu, et al

The environmental effects may limit the use of the LRGs as cosmic chronometers.  Find that there is no apparent dependence of the mean age and the SFH of quiescent LRGs on their environment, while the ages of those quiescent LRGs weakly depend on their mass.  Compare the SFHs of the SDSS LRGs with those obtained from a semi-analytical galaxy formation model, and find that they are roughly consistent with each other if considering the errors in the STARLIGHT (an SPS code)-derived ages.  Find that a small fraction of later SF in LRGs leads to a systematic overestimation (~28%) of the Hubble constant by the differential age method, and systematic errors in STARLIGHT-derived ages may lead to underestimation (~16%) of the Hubble constant.  There errors can be corrected by a detailed study of the man SFH of those LRGs and by calibrating the STARLIGHT-derived ages with those obtained independently by other methods.  The environmental effects are not significant on the age estimates of 'quiescent' LRGs, and the 'quiescent' LRGs as a population can be securely used as comic chronometers.