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Register a new userThe ALMA Patchy Deep Survey: A blind search for [CII] emitters at z~4.5
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We present a result of a blind search for [CII] 158 $mu$m emitters at $zsim 4.5$ using ALMA Cycle~0 archival data. We collected extra-galactic data covering at 330-360 GHz (band~7) from 8 Cycle~0 projects from which initial results have been already published. The total number of fields is 243 and the total on-source exposure time is 19.2 hours. We searched for line emitters in continuum-subtracted data cubes with spectral resolutions of 50, 100, 300 and 500 km/s. We could not detect any new line emitters above a 6-$sigma$ significance level. This result provides upper limits to the [CII] luminosity function at $zsim 4.5$ over $L_{rm [CII]} sim 10^8 - 10^{10} L_{odot}$ or star formation rate, SFR $sim$ 10-1000 M$_{^odot}$/yr. These limits are at least 2 orders of magnitude larger than the [CII] luminosity functions expected from the $z sim 4$ UV luminosity function or from numerical simulation. However, this study demonstrates that we would be able to better constrain the [CII] luminosity function and to investigate possible contributions from dusty galaxies to the cosmic star-formation rate density by collecting Cycle~1+2 archival data as the ALMA Patchy Deep Survey.
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The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Band 6 scan (212-272 GHz) covers potential [CII] emission in galaxies at $6leq z leq8$ throughout a 2.9 arcmin$^2$ area. By selecting on known Lyman-$alpha$ emitters (LAEs) and photometric dropout galaxies in the field, we perform targeted searches down to a 5$sigma$ [CII] luminosity depth $L_{mathrm{[CII]}}sim2.0times10^8$ L$_{odot}$, corresponding roughly to star formation rates (SFRs) of $10$-$20$ M$_{odot}$ yr$^{-1}$ when applying a locally calibrated conversion for star-forming galaxies, yielding zero detections. While the majority of galaxies in this sample are characterized by lower SFRs, the resulting upper limits on [CII] luminosity in these sources are consistent with the current literature sample of targeted ALMA observations of $z=6$-$7$ LAEs and Lyman-break galaxies (LBGs), as well as the locally calibrated relations between $L_{mathrm{[CII]}}$ and SFR -- with the exception of a single [CII]-deficient, UV luminous LBG. We also perform a blind search for [CII]-bright galaxies that may have been missed by optical selections, resulting in an upper limit on the cumulative number density of [CII] sources with $L_{mathrm{[CII]}}>2.0times10^8$ L$_{odot}$ ($5sigma $) to be less than $1.8times10^{-4}$ Mpc$^{-3}$ (90% confidence level). At this luminosity depth and volume coverage, we present an observed evolution of the [CII] luminosity function from $z=6$-$8$ to $zsim0$ by comparing the ASPECS measurement to literature results at lower redshift.
We report the results of a search for serendipitous [CII] 157.74$mu$m emitters at $zsim4.4$-$4.7$ using the Atacama Large Millimeter/submillimeter Array (ALMA). The search exploits the AS2UDS continuum survey, which covers ~50 arcmin$^2$ of the sky towards 695 luminous ($S_{870}gtrsim1$mJy) submillimeter galaxies (SMGs), selected from the SCUBA-2 Cosmology Legacy Survey (S2CLS) 0.96deg$^2$ Ultra Deep Survey (UDS) field. We detect ten candidate line emitters, with an expected false detection rate of ten percent. All of these line emitters correspond to 870$mu$m continuum-detected sources in AS2UDS. The emission lines in two emitters appear to be high-J CO, but the remainder have multi-wavelength properties consistent with [CII] from $zsimeq4.5$ galaxies. Using our sample, we place a lower limit of $>5times10^{-6}$Mpc$^{-3}$ on the space density of luminous ($L_{rm IR} simeq 10^{13}$Lsun) SMGs at $z=4.40$-$4.66$, suggesting $ge7$percent of SMGs with $S_{870mu{rm m}}gtrsim1$mJy lie at $4<z<5$. From stacking the high-resolution ($sim0.15$ full-width half maximum) ALMA $870mu$m imaging, we show that the [CII] line emission is more extended than the continuum dust emission, with an average effective radius for the [CII] of $r_{rm e} = 1.7^{+0.1}_{-0.2}$kpc compared to $r_{rm e} = 1.0pm0.1$kpc for the continuum (rest-frame $160mu$m). By fitting the far-infrared photometry for these galaxies from $100$-$870mu$m, we show that SMGs at $zsim4.5$ have a median dust temperature of $T_{rm d}=55pm4$K. This is systematically warmer than $870mu$m-selected SMGs at $zsimeq2$, which typically have temperatures around $35$K. These $zsimeq4.5$ SMGs display a steeper trend in the luminosity-temperature plane than $zle2$ SMGs. We discuss the implications of this result in terms of the selection biases of high redshift starbursts in far-infrared/submillimeter surveys.
We report the detection of [CII]158um emission from a system of three closely-separated sources in the COSMOS field at z~4.56, as part of the ALMA Large Program to INvestigate CII at Early times (ALPINE). The two dominant sources are closely associated, both spatially (1.6~11kpc) and in velocity (~100km/s), while the third source is slightly more distant (2.8~18kpc, ~300km/s). The second strongest source features a slight velocity gradient, while no significant velocity gradient is seen in the other two sources. Using the observed [CII] luminosities, we derive a total log(SFR_[CII]/[Msol/year])=2.8+/-0.2, which may be split into contributions of 59%, 31%, and 10% from the central, east, and west sources, respectively. Comparison of these [CII] detections to recent zoom-in cosmological simulations suggests an ongoing major merger. We are thus witnessing a system in a major phase of mass build-up by merging, including an on-going major merger and an upcoming minor merger, which is expected to end up in a single massive galaxy by z~2.5.
We present a survey of the [CII] 158 $mu$m line and underlying far-infrared (FIR) dust continuum emission in a sample of 27 z>6 quasars using the Atacama Large Millimeter Array (ALMA) at ~1 resolution. The [CII] line was significantly detected (at >5-sigma) in 23 sources (85%). We find typical line luminosities of $L_{rm [CII]}=10^{9-10}$ L$_odot$, and an average line width of ~385 km/s. The [CII]-to-far-infrared luminosity ratio ([CII]/FIR) in our sources span one order of magnitude, highlighting a variety of conditions in the star-forming medium. Four quasar host galaxies are clearly resolved in their [CII] emission on a few kpc scales. Basic estimates of the dynamical masses of the host galaxies give masses between $2times10^{10}$ and $2times10^{11}$ M$_odot$, i.e., more than an order of magnitude below what is expected from local scaling relations, given the available limits on the masses of the central black holes ($>3times10^8$ M$_odot$, assuming Eddington-limited accretion). In stacked ALMA [CII] spectra of individual sources in our sample, we find no evidence of a deviation from a single Gaussian profile. The quasar luminosity does not strongly correlate with either the [CII] luminosity or equivalent width. This survey (with typical on-source integration times of 8 min) showcases the unparalleled sensitivity of ALMA at millimeter wavelengths, and offers a unique reference sample for the study of the first massive galaxies in the universe.
We present a search for [CII] line and dust continuum emission from optical dropout galaxies at $z>6$ using ASPECS, our ALMA Spectroscopic Survey in the Hubble Ultra-Deep Field (UDF). Our observations, which cover the frequency range $212-272$ GHz, encompass approximately the range $6<z<8$ for [CII] line emission and reach a limiting luminosity of L$_{rm [CII]}sim$(1.6-2.5)$times$10$^{8}$ L$_{odot}$. We identify fourteen [CII] line emitting candidates in this redshift range with significances $>$4.5 $sigma$, two of which correspond to blind detections with no optical counterparts. At this significance level, our statistical analysis shows that about 60% of our candidates are expected to be spurious. For one of our blindly selected [CII] line candidates, we tentatively detect the CO(6-5) line in our parallel 3-mm line scan. None of the line candidates are individually detected in the 1.2 mm continuum. A stack of all [CII] candidates results in a tentative detection with $S_{1.2mm}=14pm5mu$Jy. This implies a dust-obscured star formation rate (SFR) of $(3pm1)$ M$_odot$ yr$^{-1}$. We find that the two highest--SFR objects have candidate [CII] lines with luminosities that are consistent with the low-redshift $L_{rm [CII]}$ vs. SFR relation. The other candidates have significantly higher [CII] luminosities than expected from their UV--based SFR. At the current sensitivity it is unclear whether the majority of these sources are intrinsically bright [CII] emitters, or spurious sources. If only one of our line candidates was real (a scenario greatly favored by our statistical analysis), we find a source density for [CII] emitters at $6<z<8$ that is significantly higher than predicted by current models and some extrapolations from galaxies in the local universe.
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