Molecular Lines as Diagnostics of High Redshift Objects

Models are presented for CO rotational line emission by high redshift starburst galaxies. The influence of the cosmic microwave background on the thermal balance and the level populations of atomic and molecular species is explicitly included. Predictions are made for the observability of starburst galaxies through line and continuum emission between z=5 and z=30. It is found that the Millimeter Array could detect a starburst galaxy with ~10^5 Orion regions, corresponding to a star formation rate of about 30 Mo yr^{-1}, equally well at z=5 or z=30 due to the increasing cosmic microwave background temperature with redshift. Line emission is a potentially more powerful probe than dust continuum emission of very high redshift objects.Comment: 15 pages LaTex, uses aasms4.sty, Accepted by ApJ

Far-Infrared and Sub-Millimeter Observations and Physical Models of the Reflection Nebula Ced 201

ISO [C II] 158 micron, [O I] 63 micron, and H_2 9 and 17 micron observations are presented of the reflection nebula Ced 201, which is a photon-dominated region illuminated by a B9.5 star with a color temperature of 10,000 K (a cool PDR). In combination with ground based [C I] 609 micron, CO, 13CO, CS and HCO+ data, the carbon budget and physical structure of the reflection nebula are constrained. The obtained data set is the first one to contain all important cooling lines of a cool PDR, and allows a comparison to be made with classical PDRs. To this effect one- and three-dimensional PDR models are presented which incorporate the physical characteristics of the source, and are aimed at understanding the dominant heating processes of the cloud. The contribution of very small grains to the photo-electric heating rate is estimated from these models and used to constrain the total abundance of PAHs and small grains. Observations of the pure rotational H_2 lines with ISO, in particular the S(3) line, indicate the presence of a small amount of very warm, approximately 330 K, molecular gas. This gas cannot be accommodated by the presented models.Comment: 32 pages, 7 figures, in LaTeX. To be published in Ap

Detection of a large fraction of atomic gas not associated with star-forming material in M17 SW

We probe the column densities and masses traced by the ionized and neutral atomic carbon with spectrally resolved maps, and compare them to the diffuse and dense molecular gas traced by [C I] and low-$J$ CO lines toward the star-forming region M17SW. We mapped a 4.1pc x 4.7pc region in the [C I] 609 m$\mu$ line using the APEX telescope, as well as the CO isotopologues with the IRAM 30m telescope. We analyze the data based on velocity channel maps that are 1 km/s wide. We correlate their spatial distribution with that of the [C II] map obtained with SOFIA/GREAT. Optically thin approximations were used to estimate the column densities of [C I] and [C II] in each velocity channel. The spatial distribution of the [C I] and all CO isotopologues emission was found to be associated with that of [C II] in about 20%-80% of the mapped region, with the high correlation found in the central (15-23 km/s ) velocity channels. The excitation temperature of [C I] ranges between 40 K and 100 K in the inner molecular region of M17 SW. Column densities in 1 km/s channels between ~10$^{15}$ and ~10$^{17}$ cm$^{-2}$ were found for [C I]. Just ~20% of the velocity range (~40 km/s) that the [C II] line spans is associated with the star-forming material traced by [C I] and CO. The total gas mass estimated from the [C II] emission gives a lower limit of ~4.4x10$^3$ $M_{\odot}$. At least 64% of this mass is not associated with the star-forming material in M17SW. We also found that about 36%, 17%, and 47% of the [C II] emission is associated with the HII, HI, and H_2 regimes, respectively. Comparisons with the H41$\alpha$ line shows an ionization region mixed with the neutral and part of the molecular gas, in agreement with the clumped structure and dynamical processes at play in M17SW. These results are also relevant to extra-galactic studies in which [C II] is often used as a tracer of star-forming material.Comment: 21 pages + 6 pages of appendix, 32 figures in total, accepted for publication on A&A (10/12/2014) Relevant calibrated data cubes are available on CD

Search for Interstellar Water in the Translucent Molecular Cloud toward HD 154368

We report an upper limit of 9 x 10^{12} cm-2 on the column density of water in the translucent cloud along the line of sight toward HD 154368. This result is based upon a search for the C-X band of water near 1240 \AA carried out using the Goddard High Resolution Spectrograph of the Hubble Space Telescope. Our observational limit on the water abundance together with detailed chemical models of translucent clouds and previous measurements of OH along the line of sight constrain the branching ratio in the dissociative recombination of H_3O+ to form water. We find at the $3\sigma$ level that no more than 30% of dissociative recombinations of H_3O+ can lead to H_2O. The observed spectrum also yielded high-resolution observations of the Mg II doublet at 1239.9 \AA and 1240.4 \AA, allowing the velocity structure of the dominant ionization state of magnesium to be studied along the line of sight. The Mg II spectrum is consistent with GHRS observations at lower spectral resolution that were obtained previously but allow an additional velocity component to be identified.Comment: Accepted by ApJ, uses aasp

Models for Dusty Lyman alpha Emitters at High Redshift

Models are presented for the Lyman alpha emission of dusty high-redshift galaxies by combining the Press-Schechter formalism with a treatment of the inhomogeneous dust distribution inside galaxies. It is found that the amount of Lyman alpha radiation escaping from the galaxies strongly depends on the time over which the dust is produced through stellar activity, and on the ambient inhomogeneity of the HII regions that surround the ionizing OB stars. Good agreement is found with recent observations, as well as previous non-detections. Our models indicate that the dust content builds up in no more than approximately 5x10^8 yr, the galactic HII regions are inhomogeneous with a cloud covering factor of order unity, and the overall star formation efficiency is at least about 5%. It is predicted that future observations can detect these Lyman alpha galaxies upto redshifts of about 8.Comment: 16 pages, 4 figures, submitted to Ap

The nature of the ISM in galaxies during the star-formation activity peak of the Universe

We combine a semi-analytic model of galaxy formation, tracking atomic and molecular phases of cold gas, with a three-dimensional radiative-transfer and line tracing code to study the sub-mm emission from atomic and molecular species (CO, HCN, [CI], [CII], [OI]) in galaxies. We compare the physics that drives the formation of stars at the epoch of peak star formation (SF) in the Universe (z = 2.0) with that in local galaxies. We find that normal star-forming galaxies at high redshift have much higher CO-excitation peaks than their local counterparts and that CO cooling takes place at higher excitation levels. CO line ratios increase with redshift as a function of galaxy star-formation rate, but are well correlated with H2 surface density independent of redshift. We find an increase in the [OI]/[CII] line ratio in typical star-forming galaxies at z = 1.2 and z = 2.0 with respect to counterparts at z = 0. Our model results suggest that typical star-forming galaxies at high redshift consist of much denser and warmer star-forming clouds than their local counterparts. Galaxies belonging to the tail of the SF activity peak at z = 1.2 are already less dense and cooler than counterparts during the actual peak of SF activity (z = 2.0). We use our results to discuss how future ALMA surveys can best confront our predictions and constrain models of galaxy formation.Comment: 19 pages, 14 figures, accepted for publication in MNRA

L-band ATS 5/Orion/S. S. Manhattan marine navigation and communication experiment Final report

L-band signals relayed by synchronous satellite for navigation and data communicatio

Search for grain growth towards the center of L1544

In dense and cold molecular clouds dust grains are surrounded by thick icy mantles. It is however not clear if dust growth and coagulation take place before the switch-on of a protostar. This is an important issue, as the presence of large grains may affect the chemical structure of dense cloud cores, including the dynamically important ionization fraction, and the future evolution of solids in protoplanetary disks. To study this further, we focus on L1544, one of the most centrally concentrated pre-stellar cores on the verge of star formation, and with a well-known physical structure. We observed L1544 at 1.2 and 2 mm using NIKA, a new receiver at the IRAM 30 m telescope, and we used data from the Herschel Space Observatory archive. We find no evidence of grain growth towards the center of L1544 at the available angular resolution. Therefore, we conclude that single dish observations do not allow us to investigate grain growth toward the pre-stellar core L1544 and high sensitivity interferometer observations are needed. We predict that dust grains can grow to 200 $\mu$m in size toward the central ~300 au of L1544. This will imply a dust opacity change by a factor of ~2.5 at 1.2 mm, which can be detected using the Atacama Large Millimeter and submillimeter Array (ALMA) at different wavelengths and with an angular resolution of 2".Comment: 12 pages, 14 figures. Accepted for publication in A&

The first frost in the Pipe Nebula

Spectroscopic studies of ices in nearby star-forming regions indicate that ice mantles form on dust grains in two distinct steps, starting with polar ice formation (H2O rich) and switching to apolar ice (CO rich). We test how well the picture applies to more diffuse and quiescent clouds where the formation of the first layers of ice mantles can be witnessed. Medium-resolution near-infrared spectra are obtained toward background field stars behind the Pipe Nebula. The water ice absorption is positively detected at 3.0 micron in seven lines of sight out of 21 sources for which observed spectra are successfully reduced. The peak optical depth of the water ice is significantly lower than those in Taurus with the same visual extinction. The source with the highest water-ice optical depth shows CO ice absorption at 4.7 micron as well. The fractional abundance of CO ice with respect to water ice is 16+7-6 %, and about half as much as the values typically seen in low-mass star-forming regions. A small fractional abundance of CO ice is consistent with some of the existing simulations. Observations of CO2 ice in the early diffuse phase of a cloud play a decisive role in understanding the switching mechanism between polar and apolar ice formation.Comment: 17 pages, 8 figures, accepted by A&

The Response of Metal Rich Gas to X-Ray Irradiation from a Massive Black Hole at High Redshift: Proof of Concept

Observational studies show that there is a strong link between the formation and evolution of galaxies and the growth of supermassive black holes (SMBH) at their centers. However, the underlying physics of this observed relation is poorly understood. In order to study the effects of X-ray radiation on the surroundings of the black hole, we implement X-ray Dominated Region (XDR) physics into Enzo and use the radiation transport module Moray to calculate the radiative transfer for a polychromatic spectrum. In this work, we investigate the effects of X-ray irradiation, produced by a central massive black hole (MBH) with a mass of M = 5x10^4 M_(solar), on ambient gas with solar and zero metallicity. We find that in the solar metallicity case, due to high opacity of the metals, the energy deposition rate in the central region (< 20 pc) is high and hence the temperatures in the center are on the order of 10^(5-7) K. Moreover, due to the cooling ability and high intrinsic opacity of solar metallicity gas, column densities of 10^(24) cm^(-2) are reached at a radius of 20 pc from the MBH. These column densities are about 3 orders of magnitudes higher than in the zero metallicity case. Furthermore, in the zero metallicity case an X-ray induced H II region is formed already after 5.8 Myr. This causes a significant outflow of gas (~8x10^6 M_(solar) from the central region, with the gas reaching outflow velocities up to ~100 km s^(-1). At later times, ~23 Myr after we insert the MBH, we find that the solar metallicity case also develops an X-ray induced H II region, but delayed by ~17 Myr.Comment: 27 pages, 11 figures. Resubmitted to Ap