Day 595

Sunday.  Monday.

1402.0510
Physical properties of emission-line galaxies at z~2 from near-infrared spectroscopy with Magellan FIRE
Masters et al

Results from NIR spectroscopy of 26 emission-line galaxies at z~2, selected from WISP survey, which uses the NIR grism of HST WFC3 to detect emission-line galaxies over 0.3<z<2.3.  The FIRE follow-up spectroscopy (R~5000) over 1.0-2.5 micron permits detailed measurements of physical properties of the z~2 emission-line galaxies.  Dust-corrected SFRs for the sample range from ~5-100 Msun/yr.  Derive a median metallicity for the sample of ~0.45 Z_sun, and the estimated stellar masses range from ~1e8.5-9.5 Msun.  The average ionization parameters measured for the sample are typically much higher than what is found for local SF galaxies.  Derive composite spectra from the FIRE sample, from which typical nebular electron densities of ~100-400 cm^-3 is implied. Based on the location of the galaxies and composite spectra on BPT diagrams, do not find evidence for significant AGN activity in the sample.  Most of the galaxies as well as the composites are offset in the BPT diagram toward higher [OIII]/H-beta at a given [NII]/H-alpha, in agreement with other observations of z>1 SF galaxies, but composite spectra derived from the sample do not show an appreciable offset from the local SF sequence on the [OIII]/H-beta versus [SII]/H-alpha diagram.  Infer a high nitrogen-to-oxygen abundance ratio from the composite spectrum, which may contribute to the offset of the high-redshift galaxies from the local SF sequence in the [OIII]/H-beta versus [NII]/H-alpha diagram.  Speculate that the elevated nitrogen abundance could result from substantial numbers of WR stars in star bursting galaxies at z~2.

1402.5145
The nebular emission of star-forming galaxies in a hierarchical universe
Orsi, et al

Predict nebular emission from SF galaxies within a cosmological galaxy formation model.  Computed by combining the SAM SAG with the photo-ionization code MAPPINGS-III.  Characterize the ISM of galaxies by relating the ionization parameter of gas in galaxies to their cold gas metallicity.  Model is in reasonable agreement with the observed H-alpha, [OII] and [OIII] LFs.  Also, the model reproduces the SF sequence of the BPT diagram for local galaxies and the observed H-alpha to [OII] line ratios at high z.  The average ionization parameter predicted for galaxies is found to increase in galaxies with low SFRs and also towards higher redshifts, in agreement with recent observational results.  Study the relation between the SFR of galaxies and their emission line luminosities as a function of z, finding strong correlation between different emission lines and their SFRs.  Present scaling relations that can be used to infer the SFR using only single line luminosities.  Model predicts that high z emission line galaxies have modest clustering bias, and thus reside in by DM haloes of masses below M<1e12 Msun/h, consistent with observational estimates of the clustering of emission lines.  Present predictions for the number of SF galaxies that can be detected at z up to ~10 by targeting different FIR emission lines with sub millimeter facilities such as ALMA.  Discuss the limitations of modeling technique and the possible ways to extend it.

1402.5151
Simulated galaxy interactions as probes of merger spectral energy distributions
Lanz, … Hernquist, et al

First systematic comparison of UV-millimeter SEDs of observed and simulated interacting galaxies.  Sample drawn from from Spitzer Interactive Galaxy Survey, and probes a range of galaxy interaction parameters.  Use 31 galaxies in 14 systems which have been observed with Herschel, Spitzer, GALEX, and 2MASS.  Create a suite of GADGET-3 hydrodynamic simulations of isolated and interacting galaxies with stellar masses comparable to those in the sample of interacting galaxies.  Photometry for the simulated systems is then calculated with the SUNRISE radiative transfer code for comparison with the observed systems.  For most of the observed systems, one or more of the simulated SEDs match reasonably well.  The best matches recover the IR luminosity and the SFR of the observed systems, and the more massive systems preferentially match SEDs from simulations of more massive galaxies.  The most morphologically distorted systems in the sample are best matched to simulated SEDs close to coalescence, while less evolved systems match well with SEDs over a wide range of interaction stages, suggesting that an SED alone is insufficient to identify interaction stage except during the most active phases in strongly interacting systems.  This result is supported by findings that the SEDs calculated for simulated systems vary little over the interaction sequence.

1402.5219
Galaxies in HI 21-cm absorption at z<3.5
Gupta et al

21-cm observation to trace the evolution of cold gas in galaxies, using ~130 sight lines.  Find that within the the measurement uncertainty, the 21-cm detection rate in strong MgII systems is constant over 0.5<z<1.5.  Since stellar feedback processes are expected to diminish the filling factor of CNM over 0.5<z<1, this lack of evolution in the 21-cm detection rate in MgII absorbers is intriguing.  Further, find that if the majority of 21-cm absorbers arise from DLAs then the cross-section of 21-cm absorbing gas i.e., cold neutral medium amongst DLAs has increased from z=3.5 to z=0.5.  In a samples of 13 z>2 DLAs with both 21-cm and H2 absorption measurements, report two new H2 detections and find that in 8/13 cases neither 21-cm nor H2 is detected.  This confirms that the HI gas in z>2 DLAs is predominantly warm.  There are 2 cases where 21cm absorption is not detected despite the presence of H2 with evidence for the presence of cold gas.  This can be explained if H2 components seen in DLA are compact (15 pc) and contain <10% of the total N(HI).  Briefly discuss results from ongoing survey to identify 21-cm absorbers at low-z to establish connection between 21-cm absorbers and galaxies, and constrain the extent of absorbing gas.

1402.5333
The phases of water ice in the solar nebula
Ciesla

Show that amorphous ice formed more readily than previously recognized, with formation temperatures <70 K being possible under protoplanetary disk conditions.  Further argue that photodesorption and freeze-out of water molecules near the surface layers of the solar nebular would have provided the conditions needed for amorphous ice to form.  This processing would be a natural consequence of ice dynamics, and would allow for the trapping of noble gases and other volatiles in water ice in the outer solar nebula.