Saturday.
1307.6559
The optical green valley vs mid-IR canyon in compact groups
Walker ... Zabuldoff, et al
Compact groups of galaxies provide conditions similar to those experienced by galaxies in the earlier universe [why?]. Recent work on compact groups has led to the discovery of a dearth of mid-IR transition galaxies (MIRTGs) in IRAC (3.6-8.0 micron) color space, as well as at intermediate sSFRs. But find that in compact groups these MIR transition galaxies in the MIR dearth have already transitioned to the optical (i.e., [g-r]) red sequence. Investigate the optical CMD of 99 compact groups containing 348 galaxies and compare the optical CMD with MIR color space for compact group galaxies. Utilizing redshifts available from SDSS, identify new galaxies members for 6 groups. By combining optical and MIR data, obtain information on both the dust and the stellar populations in compact group galaxies. Also compare with more isolated galaxies and galaxies in the Coma cluster, reveal (similarly to clusters) compact groups are dominated by optically red galaxies. Find that compact group transition galaxies [at what redshift range are they?] lie on the optical red sequence, LVL+SINGS MIR transition galaxies span the range of optical colors. The dearth of IMR transition galaxies in compact groups may be due to a lack of moderately SFing low mass galaxies; the relative lack of these galaxies could be due to their relatively small gravitational potential wells. This makes them more susceptible to this dynamic environment, thus causing them to more easily lose gas or be accreted by larger members.
1307.6563
The specific frequency and the globular cluster formation efficiency in Milgromian dynamiacs
Wu, Kroupa
There appears to be a universal specific GC formation efficiency eta which relates the total mass of GCs to the virial mass of host DM haloes M_vir (recent studies). Drive specific frequency [?] and specific GC formation efficiency eta derived as a function of M_vir in Milgromian dynamics (MOND). In MOND, for galaxies with M_vir <=1e12 Msun, eta decreases with the increase of M_vir, while for massive galaxies eta increases with the increase of M_vir. (If you assume DM exists, you would incorrectly infer a universal constant fraction between mass of the GC system and a "false" DM halo of the baryonic galaxy.)
1307.6565
The preferentially magnified active nucleus in IRAS F10214+4724 -
I., Lens model and spatially resolved radio emission,
II. spatially resolved cold molecular gas,
III. VLBI observations of the radio core
Deane, ... Marshall et al
I. Lensing model suggests magnifications of 15-20, smaller than mu=50-100 often used for this lensed ULIRG system.
II. Observation of cold (CO (1-0)) molecular gas in a lensed ULIRG at z=2.3 with an obscured active nucleus. The galaxy is spatially and spectrally well-resolved in the CO (1-0) emission line. Counter image detected at 3 sigma. SED resolved, see linear arrangement (tentatively a rotating disk). Predict a distortion of the CO SLED (spectral line energy distribution) where higher order J lines that may be partially excited by AGN heating will be preferentially lensed owing to their smaller solid angles and closer proximity to the AGN and therefore the cusp of the caustic. Comparison with other lensing inversion results shows that the narrow line regions and AGN radio core are preferentially lensed by a factor ~3 and 11 respectively, relative to the (cool) molecular gas emission. This distorts the global continuum emission SED and suggests caution in unsophisticated uses of IRAS F102114+4724 as an archetype of high-z ULRIG. Present tentative evidence for an extended, low excitation cold gas component that implies that the total molecular gas mass in this galaxy is a factor of >2x greater than that calculated using spatially unresolved CO observations.
III. Lensing allows effective angular resolution of 50 pc at z=2.3. Estimate quasar bolometric luminosity from a number of independent techniques; find evidence that the AGN may be close to Compton-thick, with an intrinsic bolometric luminosity of 1e11.34 L_sun. Make SMBH mass estimate and find 1e8.36 Msun, suggesting a low BH accretion rate. Find evidence for M_BH/M_spheroid ratio that is 1-2 orders of magnitude larger than that of SMGs at z~2. At face value, suggests that this system has undergone a different evolutionary path compared to SMGs at the same epoch. A primary result of this work is the demonstration that emission regions of differing size and position can undergo significantly different magnification boosts (>1 dex) and therefore distort the high-z view of gravitationally lensed galaxies.
1307.6575
Cosmic ray acceleration in young supernova remnants
Schure, Bell
Investigate appearance of B-field amplification resulting from CR escape current in the context of SNe remnant shock waves. The current is inversely proportional to the maximum energy of CRs, and is a strong function of the shock velocity. Depending on the evolution of the shock wave (drastically different for different circumstellar environments), the maximum energy of CRs as required to generate enough current to trigger the "non-resonant hybrid instability" [what is that?] that confines the CRs follows a different evolution and reaches different values. Find that the best candidates to accelerate CRs to ~few PeV energies are young remnants in a dense environment, such as a red supergiant wind, as may be applicable to Cass A. Also find that for a typical BG B-field strength of 5 microG the instability is quenched in about 1000 years, making SN1006 just at the border of candidates for CR acceleration to high energies.
1307.6588
Metal-poor, cool gas in the circumgalactic medium of a z=2.4 star-forming galaxy: direct evidence for cold accretion?
Crighton, Hennawi, Prochaska
Current galaxy formation paradigm: high-z galaxies are predominantly fuelled by accretion of cool, metal-poor gas from IGM. Hydro sims predict that this material should be observable in absorption against BG sightlines within a galaxy's virial radius as optically thick lyman-lymit systems (LLSs) with low metallicities. Report the discovery of exactly such a strong metal-poor absorber at an impact parameter R_perp = 58 kpc from a SF galaxy at z=2.44. Besides strong neutral hydrogen [N(HI)=1e19.5 cm^-2], detect neutral deuterium and oxygen, allowing a precise measurement of the metallicity: log10(Z/Zsolar)=-2.0, or 7-15e-3 solar. Furthermore, the narrow deuterium linewidth requires a cool temperature <20,000 K. Given the striking similarities between this system and the predictions of simulations, argue that it represents the direct detection of a high redshift cold-accretion stream. The low metallicity gas cloud is a single component of an absorption system exhibiting a complex velocity, ionization, and enrichment structure. Two other components have metallicities >0.1 solar, 10x larger than the metal-poor component. Conclude that the photoionized CGM of this galaxy is highly inhomogeneous: the majority of the gas is in a cool, metal-poor and predominantly neutral phase, but the majority of the metals are in a highly-ionized phase exhibiting weak neutral hydrogen absorption but strong metal absorption. If such inhomogeneity is common, then high-resolution spectra and detailed ionization modeling are critical to accurately appraise the distribution of metals in the high-z CGM.
1307.6643
The pre-merger impact velocity of the binary cluster A1750 from X-ray, lensing and hydrodynamical simulations
Molnar, Chiu, Broadhurst, Stadel
Study initial velocity conditions of merging cluster pairs (as the IC affects the final collision velocity, which seems to be too large in cases of Bullet cluster or similar cluster collisions). Use Chandra data confirming a significant increase in the projected X-ray temperature between the two cluster centers in A1750 consistent with expectations for a merging cluster. Model this system with a self-consistent hydrodynamical simulation of DM and gas using the FLASH code. Simulations reproduce well the X-ray data, and the measured redshift difference between the two clusters in the phase before the first core passage viewed at an intermediate projection angle. The deprojected initial relative velocity derived using this model is 1460 km/s which is considerably higher than the predicted mean impact velocity for simulated massive haloes derived by recent LCDM cosmological simulations [!], but it is within the allowed range. Simulations demonstrate that such systems can be identified using a multi-wavelength approach and numerical simulations, for which the statistical distribution of relative impact velocities may provide a definitive examination of a broad range of DM scenarios.
1307.6815
Planck intermediate results. XIV. Dust emission at millimetre wavelengths in the galactic plane
Planck Collaboration
Planck HFI data combined with ancillary radio data to study the emissivity index of the interstellar dust emission in the frequency range 3-0.8 mm in the Galactic plane. Analyse the region l=20-44 deg, and |b| <= 4 deg where the free-free emission can be estimated from radio recombination line data. Fit the spectra at each sky pixel with a modified blackbody model and two spectral indices, beta_mm and beta_FIR, below and above 353 GHz respectively. Find that beta_mm is smaller than beta_FIR and detect a correlation between this low frequency power-law index and the dust optical depth at 353 GHz, tau_353. beta_mm increases from about 1.53 in the more diffuse regions of the Galactic disk, |b|=3-4 deg and and tau_353~5e-5, to about 1.65 in the densest regions with an optical depth of more than one order of magnitude higher. Associate this correlation with an evolution of the dust emissivity related to the fraction of molecular gas among the line of sight. This translates into beta_mm~1.53 for a medium which is mostly atomic and beta_mm~1.65 when the medium is dominated by molecular gas. Find that the both the 2-level system model and the emission by ferromagnetic particles can explain the results if spatial variations of the component of physical processes responsible for the flattening of the dust emission are allowed. The results improve the understanding of the physics of interstellar dust, and lead towards a complete model of the dust spectrum from FIR to millimeter wavelengths.
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