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Register a new userThe ALMA Spectroscopic Survey in the HUDF: A Search for [CII] Emitters at $6 leq z leq 8$
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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.
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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.
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.
Using the near-IR spectroscopy of the MOSFIRE Deep Evolution Field (MOSDEF) survey, we investigate the role of local environment in the gas-phase metallicity of galaxies. The local environment measurements are derived from accurate and uniformly calculated photometric redshifts with well-calibrated probability distributions. Based on rest-frame optical emission lines, [NII]$lambda6584$ and H$alpha$, we measure gas-phase oxygen abundance of 167 galaxies at $1.37leq zleq1.7$ and 303 galaxies at $2.09leq zleq2.61$, located in diverse environments. We find that at $zsim1.5$, the average metallicity of galaxies in overdensities with $M_*sim10^{9.8}M_odot, 10^{10.2}M_odot$ and $10^{10.8}M_odot$ is higher relative to their field counterparts by $0.094pm0.051$, $0.068pm0.028$ and $0.052pm0.043$ dex, respectively. However, this metallicity enhancement does not exist at higher redshift, $zsim2.3$, where, compared to the field galaxies, we find $0.056pm0.043$, $0.056pm0.028$ and $0.096pm 0.034$ dex lower metallicity for galaxies in overdense environments with $M_*sim10^{9.8}M_odot, 10^{10.2}M_odot$ and $10^{10.7}M_odot$, respectively. Our results suggest that, at $1.37leq zleq2.61$, the variation of mass-metallicity relation with local environment is small ($<0.1$dex), and reverses at $zsim2$. Our results support the hypothesis that, at the early stages of cluster formation, owing to efficient gas cooling, galaxies residing in overdensities host a higher fraction of pristine gas with prominent primordial gas accretion, which lowers their gas-phase metallicity compared to their coeval field galaxies. However, as the Universe evolves to lower redshifts ($zlesssim2$), shock-heated gas in overdensities cannot cool down efficiently, and galaxies become metal-rich rapidly due to the suppression of pristine gas inflow and re-accretion of metal-enriched outflows in overdensities.
Using the CANDELS photometric catalogs for the HST/ACS and WFC3, we identified massive evolved galaxies at $3 < z < 4.5$, employing three different selection methods. We find the comoving number density of these objects to be $sim 2 times 10^{-5}$ and $8 times 10^{-6}Mpc^{-3}$ after correction for completeness for two redshift bins centered at $z=3.4, 4.7$. We quantify a measure of how much confidence we should have for each candidate galaxy from different selections and what are the conservative error estimates propagated into our selection. Then we compare the evolution of the corresponding number densities and their stellar mass density with numerical simulations, semi-analytical models, and previous observational estimates, which shows slight tension at higher redshifts as the models tend to underestimate the number and mass densities. By estimating the average halo masses of the candidates ($M_h approx 4.2, 1.9, 1.3 times 10^{12} M_odot$ for redshift bins centered at $z=3.4, 4.1, 4.7$), we find them to be consistent with halos that were efficient in turning baryons to stars and were relatively immune to the feedback effects and on the verge of transition into hot-mode accretion. This can suggest the relative cosmological starvation of the cold gas followed by an overconsumption phase in which the galaxy consumes the available cold gas rapidly as one of the possible drivers for the quenching of the massive evolved population at high redshift.
We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at 0.5 $leq z leq$ 1.5 in the rest-frame far-ultraviolet (FUV) using HST WFC3 broadband imaging in F225W, F275W, and F336W. An analysis of 1,404 galaxies yields 209 galaxies that host 403 kpc-scale clumps. These host galaxies appear to be typical star-forming galaxies, with an average of 2 clumps per galaxy and reaching a maximum of 8 clumps. We measure the photometry of the clumps, and determine the mass, age, and star formation rates (SFR) utilizing the SED-fitting code FAST. We find that clumps make an average contribution of 19% to the total rest-frame FUV flux of their host galaxy. Individually, clumps contribute a median of 5% to the host galaxy SFR and an average of $sim$4% to the host galaxy mass, with total clump contributions to the host galaxy stellar mass ranging widely from less than 1% up to 93%. Clumps in the outskirts of galaxies are typically younger, with higher star formation rates, than clumps in the inner regions. The results are consistent with clump migration theories in which clumps form through violent gravitational instabilities in gas-rich turbulent disks, eventually migrate toward the center of the galaxies, and coalesce into the bulge.
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