Day 538

Monday.

1310.6362
An ALMA survey of submillimetre galaxies in the extended Chandra deep field south: the far-infrared properties of SMGs
Swinbank, et al

In ECDFS, 99 SMGs in 870um (ALMA), with 24um and radio imaging of this field; deb lend Herschel/SPIRE imaging of this region to extract their FIR fluxes and colors.  The median photometric redshifts for ALMA LESS SMGs (detected in at least 2 SPIRE bands) increases with wavelength of the peak in their SEDs, with z=2.3, 2.5, 3.5 for the 250, 350 and 500um peakers respectively.  Find that 34 ALESS SMGs do not have a >3-sigma counterpart at 250, 350, or 500 um.  These galaxies have a median photometric redshift of z=3.3pm0.5, which is higher than the full ALESS SMG sample; z=2.5pm0.2.  Using the photo-z together with the 250-870um photometry, estimate the FIR luminosities and characteristic dust temperature of each SMG.  The median IR luminosity of the S_870um>2mJy SMGs is L_IR=3.0e12 Lsun (SFR=300pm30 Msun/yr).  At a fixed luminosity, the characteristic dust temperature of these high-z SMGs is 2-3K lower than comparably luminous galaxies at z=0, reflecting the more extended SF occurring in these systems.  By extrapolating the 870 um number counts to S_870um=1mJy, show that the contribution of S_870um>1mJy SMGs to the cosmic SF budget is 20% of the total over 1<z<4.  Derive a median dust mass for these SMGs of M_d=3.6e8 Msun and by adopting an appropriate gas-to-dust ratio, estimate an average molecular mass of M_H2=4.2e10 Msun.  Finally, use estimate of the H2 masses to show that SMGs with S_870um>1mJy contain ~10% of the z~2 volume-averaged H2 mass density at this epoch.

1310.6363
An ALMA survey of sub millimeter galaxies in the Extended Chandra Deep Field South: The redshift distribution and evolution of sub millimeter galaxies
Simpson, et al

Present the photo-z distribution of SMGs (unbiased sample of 870um selected objects) of 96 SMG, 77 of which have 4-19 band, optical-NIR photometry.  Model SEDs for these 77 SMGs, deriving a median photo-z of 2.3pm0.1.  The remaining 19 were stacked to confirm they are not spurious detections.  Assuming these sources have an absolute H-band magnitude distribution comparable to that of a complete sample of z~1-2 SMGs, demonstrate that the undetected SMGs lie at higher z, raising the median redshift for SMGs to z=2.5pm0.2.  Show that the proportion of galaxies undergoing and SMG phase at z>3 is 35pm5% of the total population.  Derive a median stellar mass for SMGs of M*=8e10 Msun, but caution that there are significant systematic uncertainties in M* estimates; up to x5 for individual sources.  Assuming the SF activity in SMGs has a timescale of ~100 Myr, show that their descendants at z~0 would have a space density and M_H distribution which are in good agreement with those of local ellipticals.  In addition, the inferred mass-weighted ages of the local elliptical broadly agree with the look-back times of the SMG events.  Taken together, these results are consistent with a simple model that identifies SMGs as events that form most of the stars seen in the majority of luminous elliptical galaxies at the present day.

1310.6364
An ALMA survey of sub millimeter galaxies in the Extended Chandra Deep Filed South: The AGN fraction and X-ray properties of sub millimeter galaxies
Wang et al

The large gas and dust reservoirs of SMGs could potentially provide ample fuel to trigger an AGN, but previous studies of the AGN fraction in SMGs have been controversial largely due to the inhomogeneity and limited angular resolution of the available sub millimeter surveys.  Set improved constraints on the AGN fraction and X-ray properties of the SMGs with ALMA and Chandra observations in the ECDFS.  This study is the first among similar works to have unambiguously identified the X-ray counterparts of SMGs; this is accomplished using the fully submm-identified, statistically reliable SMG catalog with 99 SMGs from the ALMA LABOCA ECDFS sub millimeter survey (ALESS).  Found 10 X-ray sources associated with SMGs (median z=2.3), of which  where identified as AGNs from cross-checking.  The other 2 X-ray detected SMGs have levels of X-ray emission that can be plausibly explained by their SF activity.  6 of the 8 SMG-AGNs are moderately/highly absorbed, with N_H>1e23 cm^-2.  An analysis of the AGN fraction, taking into account the spatial variation of X-ray sensitivity, yields an AGN fraction of 17+16-6% for AGNs with rest-frame 0.5-8 keV absorption-corrected luminosity >7.8e42 erg/s; provide estimated AGN fractions as a function of X-ray flux and luminosity.  ALMA's high angular resolution also enables direct X-ray stacking at the precise positions of SMGs for the first time, and found 4 potential SMG-AGNs in the stacking sample.

1310.6365
Dwarfs walking in a row.  The filamentary nature of the NGC3109 association
Bellazzini et al

Reconsider the association, whose members are: NGC3109, Antila, Sextans A and Sextans B.  Find that the original members of the association, together with the recently discovered and adjacent dirt Leo P, form a very tight and elongated configuration in space.  All these galaxies lie within ~100 kpc of a line that is ~1070 kpc long, from one extreme (NGC3109) to the other (Leo P), and they show a gradient in the Local Group standard of rest velocity with a total amplitude of 43 kpm/s Mpc and a rms scatter of just 16.8 km/s.  It is shown that the reported configuration is exceptional given the known dwarf galaxies in the Local Group and its surroundings.  Conclude that (a) Leo P is likely an additional member of the NGC 3109 association, and (b) the association is highly order in space and velocity, and it is very elongated, suggesting that it has been originated by a tidal interaction or it was accreted as a filamentary sub-structure.

1310.6366
Pan-STARRS1: galaxy clustering in the small area survey 2
Farrow, Cole, Metcalfe, … Kaiser, et al

PS1 is currently obtaining imaging in 5 bands (grizy) for 3pi stradian survey, one of the largest optical surveys ever conducted.  The finished survey will have spatially varying depth, due to the survey strategy.  This paper presents a method to correct galaxy number counts and galaxy clustering for this potential systematic based on a simplified signal to noise measurement.  A star and galaxy separation method calibrated using realistic synthetic images is also presented, along with an approach to mask bright stars.  By using techniques on a ~69 sq. deg. region of science verification data this paper shows PS1 measurements of the 2pt angular correlation function as a function of apparent magnitude agree with measurements from deeper, smaller surveys.  Clustering measurements appear reliable down to a magnitude limit of fps<22.5.  Additionally, stellar contamination and false detection issues are discussed and quantified.  This work is the second of two papers which pave the way for the exploitation of the full 2pi survey for studies of LSS.

1310.6367
NGC1277: a massive compact relic galaxy in the nearby Universe
Trujillo et al

As early as 10 Gyr ago [redshift?], galaxies with more than 1e11 Msun in [stellar mass] already existed.  While most of these massive galaxies must have subsequently transformed through on-going SF and mergers with other galaxies, a small fraction (<0.1%) may have survived untouched till today.  Searches for such relic galaxies, useful windows to explore the early Universe, have been inconclusive to date: galaxies with masses and sizes like those observed at high z (M*>1e11 Msun; Re<1.5 kpc) have been found in the local Universe, but their stars are far too young for the galaxy to be a relic.  This paper explores the first case of a nearby galaxy, NGC1277 (in the Perseus cluster at a distance of 73 Mpc [distance from cluster center?  or from us?]), which fulfills all the criteria to be considered a relic galaxy.  Using deep optical spectroscopy, derive the SFH along the structure of the galaxy: the stellar populations are uniformly old (>10 Gyr) with no evidence for more recent SF episodes.  The metallicity of their stars is super-solar ([Fe/H]=0.20pm0.04) and alpha enriched ([alpha/Fe]=0.4 pm 0.1).  This suggests a very short formation time scale for the bulk of stars of this galaxy.  This object also rotates very fast (Vrot~300 km/s) and has a large velocity dispersion (sigma>300 km/s).  NGC1277 will allow future explorations in full detail of properties such as the structure, internal dynamics, metallicity, dust content and IMF at around 10-12 Gyr back in time when the first massive galaxies were built.

1310.6368
The Pan-STARRS1 small area survey 2
Metcalfe et al

PS1 is acquiring multi-epoch imaging in 5 bands (grizy) over the entire sky north of declination -30 deg (the 3pi survey).  In July 2011 a test area of ~70 sq deg. was observed to the expected final depth of the main survey.  In this, the first of a series of papers targeting the galaxy count and clustering properties of the combined multi-epoch test area data, present a detailed investigation into the depth of the survey and the reliability of the PS1 analysis software.  Show that the PS1 reduction software can recover the properties of fake sources, and show good agreement between the magnitudes measured by PS1 and those from SDSS.  Also examine the number of false detections apparent in the PS1 data.  Comparisons show that the test are survey is somewhat deeper than the SDSS in all bands, and in particular, the z band approaches the depth of the stacked stripe82 data.