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Register a new user[CII] 158 Micron Emission from z~4 HI Absorption-Selected Galaxies
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Authors
Marcel Neeleman
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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.
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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.
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 consider the capabilities of ALMA and the ngVLA to detect and image the[CII] 158,$mu$m line from galaxies into the cosmic `dark ages ($z sim 10$ to 20). The [CII] line may prove to be a powerful tool in determining spectroscopic redshifts, and galaxy dynamics, for the first galaxies. In 40,hr, ALMA has the sensitivity to detect the integrated [CII] line emission from a moderate metallicity, active star-forming galaxy [$Z_A = 0.2,Z_{odot}$; star formation rate (SFR)= 5,$M_odot$,yr$^{-1}$], at $z = 10$ at a significance of 6$sigma$. The ngVLA will detect the integrated [CII] line emission from a Milky-Way like star formation rate galaxy ($Z_{A} = 0.2,Z_{odot}$, SFR = 1,$M_odot$,yr$^{-1}$), at $z = 15$ at a significance of 6$sigma$. Imaging simulations show that the ngVLA can determine rotation dynamics for active star-forming galaxies at $z sim 15$, if they exist. The [CII] detection rate in blind surveys will be slow (of order unity per 40,hr pointing.
We present high spatial-resolution (~2kpc) Atacama Large Millimeter/submillimeter Array (ALMA) observations of [CII] 158um and dust-continuum emission from a galaxy at z=3.7978 selected by its strong HI absorption (a damped Lya absorber, DLA) against a background QSO. Our ALMA images reveal a pair of star-forming galaxies separated by ~6kpc (projected) undergoing a major merger. Between these galaxies is a third emission component with highly elevated (2x) [CII] 158um emission relative to the dust continuum, which is likely to arise from stripped gas associated with the merger. This merger of two otherwise-normal galaxies is not accompanied by enhanced star-formation, contrary to mergers detected in most luminosity-selected samples. The DLA associated with the merger exhibits extreme kinematics, with a velocity width for the low-ionization metal lines of Dv90~470km/s that spans the velocity spread revealed in the [CII] 158um emission. We propose that DLAs with high Dv90 values are a signpost of major mergers in normal galaxies at high redshifts, and use the distribution of the velocity widths of metal lines in high-z DLAs to provide a rough estimate the fraction of z>3 galaxies that are undergoing a major merger.
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