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Register a new userDetectability of [CII] 158 micron emission from high-redshift galaxies: predictions for ALMA and SPICA
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Kentaro Nagamine n UCSD
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We discuss the detectability of high-redshift galaxies via [CII] 158 micron line emission by coupling an analytic model with cosmological Smoothed Particle Hydrodynamics (SPH) simulations that are based on the concordance Lambda cold dark matter (CDM) model. Our analytic model describes a multiphase interstellar medium irradiated by the far ultra-violet radiation from local star-forming regions, and it calculates thermal and ionization equilibrium between cooling and heating. The model allows us to predict the mass fraction of a cold neutral medium (CNM) embedded in a warm neutral medium (WNM). Our cosmological SPH simulations include a treatment of radiative cooling/heating, star formation, and feedback effects from supernovae and galactic winds. Using our method, we make predictions for the [CII] luminosity from high-redshift galaxies which can be directly compared with upcoming observations by the Atacama Large Millimeter Array (ALMA) and the Space Infrared Telescope for Cosmology and Astrophysics (SPICA). We find that the number density of high-redshift galaxies detectable by ALMA and SPICA via [CII] emission depends significantly on the amount of neutral gas which is highly uncertain. Our calculations suggest that, in a CDM universe, most [CII] sources at z=3 are faint objects with Snu < 0.01 mJy. Lyman-break galaxies (LBGs) brighter than R_AB=23.5 mag are expected to have flux densities Snu = 1-3 mJy depending on the strength of galactic wind feedback. The recommended observing strategy for ALMA and SPICA is to aim at very bright LBGs or star-forming DRG/BzK galaxies.
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The [CII] fine structure transition at 158 microns is the dominant cooling line of cool interstellar gas, and is the brightest of emission lines from star forming galaxies from FIR through meter wavelengths. With the advent of ALMA and NOEMA, capable of detecting [CII]-line emission in high-redshift galaxies, there has been a growing interest in using the [CII] line as a probe of the physical conditions of the gas in galaxies, and as a SFR indicator at z>4. In this paper, we use a semi-analytical model of galaxy evolution (G.A.S.) combined with the code CLOUDY to predict the [CII] luminosity of a large number of galaxies at 4< z<8. At such high redshift, the CMB represents a strong background and we discuss its effects on the luminosity of the [CII] line. We study the LCII-SFR and LCII-Zg relations and show that they do not strongly evolve with redshift from z=4 and to z=8. Galaxies with higher [CII] luminosities tend to have higher metallicities and higher star formation rates but the correlations are very broad, with a scatter of about 0.5 dex for LCII-SFR. Our model reproduces the LCII-SFR relations observed in high-redshift star-forming galaxies, with [CII] luminosities lower than expected from local LCII-SFR relations. Accordingly, the local observed LCII-SFR relation does not apply at high-z. Our model naturally produces the [CII] deficit, which appears to be strongly correlated with the intensity of the radiation field in our simulated galaxies. We then predict the [CII] luminosity function, and show that it has a power law form in the range of LCII probed by the model with a slope alpha=1. The slope is not evolving from z=4 to z=8 but the number density of [CII]-emitters decreases by a factor of 20x. We discuss our predictions in the context of current observational estimates on both the differential and cumulative luminosity functions.
We report on a search for the [CII] 158 micron emission line from galaxies associated with four high-metallicity damped Ly-alpha absorbers (DLAs) at z ~ 4 using the Atacama Large Millimeter/sub-millimeter Array (ALMA). We detect [CII] 158 micron emission from galaxies at the DLA redshift in three fields, with one field showing two [CII] emitters. Combined with previous results, we now have detected [CII] 158 micron emission from five of six galaxies associated with targeted high-metallicity DLAs at z ~ 4. The galaxies have relatively large impact parameters, ~16 - 45 kpc, [CII] 158 micron line luminosities of (0.36 - 30) x 10^8 Lsun, and rest-frame far-infrared properties similar to those of luminous Lyman-break galaxies, with star-formation rates of ~7 - 110 Msun yr-1. Comparing the absorption and emission line profiles yields a remarkable agreement between the line centroids, indicating that the DLA traces gas at velocities similar to that of the [CII] 158 micron emission. This disfavors a scenario where the DLA arises from gas in a companion galaxy. These observations highlight ALMAs unique ability to uncover a high redshift galaxy population that has largely eluded detection for decades.
Gas surrounding high redshift galaxies has been studied through observations of absorption line systems toward background quasars for decades. However, it has proven difficult to identify and characterize the galaxies associated with these absorbers due to the intrinsic faintness of the galaxies compared to the quasars at optical wavelengths. Utilizing the Atacama Large Millimeter/Submillimeter Array, we report on detections of [CII] 158 micron line and dust continuum emission from two galaxies associated with two such absorbers at a redshift of z~4. Our results indicate that the hosts of these high-metallicity absorbers have physical properties similar to massive star-forming galaxies and are embedded in enriched neutral hydrogen gas reservoirs that extend well beyond the star-forming interstellar medium of these galaxies.
Our objectives are to determine the properties of the interstellar medium (ISM) and of star-formation in typical star-forming galaxies at high redshift. Following up on our previous multi-wavelength observations with HST, Spitzer, Herschel, and the Plateau de Bure Interferometer (PdBI), we have studied a strongly lensed z=2.013 galaxy, the arc behind the galaxy cluster MACS J0451+0006, with ALMA to measure the [CII] 158 micron emission line, one of the main coolants of the ISM. [CII] emission from the southern part of this galaxy is detected at 10 $sigma$. Taking into account strong gravitational lensing, which provides a magnification of $mu=49$, the intrinsic lensing-corrected [CII]158 micron luminosity is $L(CII)=1.2 times 10^8 L_odot$. The observed ratio of [CII]-to-IR emission, $L(CII)/L(FIR) approx (1.2-2.4) times 10^{-3}$, is found to be similar to that in nearby galaxies. The same also holds for the observed ratio $L(CII)/L(CO)=2.3 times 10^3$, which is comparable to that of star-forming galaxies and active galaxy nuclei (AGN) at low redshift. We utilize strong gravitational lensing to extend diagnostic studies of the cold ISM to an order of magnitude lower luminosity ($L(IR) sim (1.1-1.3) times 10^{11} L_odot$) and SFR than previous work at high redshift. While larger samples are needed, our results provide evidence that the cold ISM of typical high redshift galaxies has physical characteristics similar to normal star forming galaxies in the local Universe.
We present the first results of an observational programme undertaken to map the fine structure line emission of singly ionized carbon ([CII] 157.7409 micron) over extended regions using a Fabry Perot spectrometer newly installed at the focal plane of a 100cm balloon-borne far-infrared telescope. This new combination of instruments has a velocity resolution of ~200 km/s and an angular resolution of 1.5. During the first flight, an area of 30x15 in Orion A was mapped. The observed [CII] intensity distribution has been compared with the velocity-integrated intensity distributions of 13CO(1-0), CI(1-0) and CO(3-2) from the literature. The observed line intensities and ratios have been analyzed using the PDR models by Kaufman et al. 1999 to derive the incident UV flux and volume density at a few selected positions.
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