arXiv subjects

J. Wagg

Publications and source records attributed to J. Wagg.

At least 19 recordsLinked to original sources

arXiv2025

Exploring the IR-radio correlation in massive galaxy clusters at the end of cosmic noon

We investigate the effect of the environment on the infrared and radio emission of cluster galaxies during the transition epoch at 1 < z < 2 when they first start to quench consistently in the majority of galaxy clusters. We considered a sample of 129 cluster member galaxies from 11 massive clusters at a confirmed redshift of 1.0-1.8 from the IRAC Shallow Cluster Survey (ISCS), the IRAC Distant Cluster Survey (IDCS), and new 3 GHz images from the Karl G. Jansky Very Large Array (VLA). We calculated the IR-radio correlation slope parameter, q, in order to identify differences in the ratios of IR to radio of cluster galaxies and field galaxy comparison samples at different redshifts. Active galactic nuclei (AGNs) were identified and analyzed to search for any effect on the IR-radio correlation. The correlation parameter values were also compared by the Kolmogorov-Smirnov test with field galaxies. Our comparison of the IR-radio correlation in cluster galaxies to the control sample of field galaxies reveals a marginally to modestly significant difference in the correlation slope parameter at the ~2sigma-3sigma level. A split of the clusters into low-redshift (1 < z < 1.37) and high-redshift (1.37 < z < 1.8) bins indicates a more significant difference in the correlation parameter in the lower redshift cluster subsample, where widespread quenching begins. We find no difference in the IR-radio correlation between galaxies that host AGNs and non-active star-forming galaxies either. This suggests that our AGNs are overwhelmingly radio quiet and therefore do not affect the results we described above. We conclude that further investigations based on larger datasets are needed to constrain the impact of the cluster environment on the IR-radio correlation better.

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arXiv2022

MASCOT: Molecular gas depletion times and metallicity gradients -- evidence for feedback in quenching active galaxies

We present results from the first public data release of the MaNGA-ARO Survey of CO Targets (MASCOT), focussing our study on galaxies whose star-formation rates and stellar masses place them below the ridge of the star-forming Main Sequence. In optically-selected type 2 AGN/LINERs/Composites, we find an empirical relation between gas-phase metallicity gradients $\nabla Z$ and global molecular gas depletion times $t_\mathrm{dep} = M_{H_2}$/SFR with "more quenched" systems showing flatter/positive gradients. Our results are based on the O3N2 metallicity diagnostic (applied to star-forming regions within a given galaxy) which was recently suggested to also be robust against emission by diffuse ionised gas (DIG) and low-ionisation nuclear emission regions (LINERs). We conduct a systematic investigation into possible drivers of the observed $\nabla Z$ - $t_\mathrm{dep}$ relation (ouflows, gas accretion, in-situ star formation, mergers, and morphology). We find a strong relation between $\nabla Z$ or $t_\mathrm{dep}$ and centralised outflow strength traced by the [OIII] velocity broadening. We also find signatures of suppressed star-formation in the outskirts in AGN-like galaxies with long depletion times and an enhancement of metals in the outer regions. We find no evidence of inflows impacting the metallicity gradients, and none of our results are found to be significantly affected by merger activity or morphology. We thus conclude that the observed $\nabla Z$ - $t_\mathrm{dep}$ relation may stem from a combination of metal redistribution via weak feedback, and a connection to in-situ star formation via a resolved mass-metallicity-SFR relation.

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arXiv2022

PRUSSIC I - a JVLA survey of HCN/HCO+/HNC (1-0) emission in z$\sim$3 dusty galaxies: Low dense-gas fractions in high-redshift star-forming galaxies

Dusty star-forming galaxies (DSFGs) at redshift z$\geq$1 are among the most vigorously star-forming galaxies in the Universe. However, their dense ($\geq$10$^5$ cm$^{-3}$ ) gas phase - typically traced by HCN(1-0) - remains almost entirely unexplored: only two DSFGs have been detected in HCN(1-0) to date. We present results of a JVLA survey of the J=1-0 transition of HCN, HCO+, and HNC(1-0) in six strongly lensed DSFGs at z = 2.5 - 3.3, effectively doubling the number of DSFGs with deep observations of these lines. We detect HCN(1-0) emission in one source (J1202+5354, 4.4$\sigma$), with a tentative HCO+ (1-0) detection in another (J1609+6045, 3.3$\sigma$). Spectral stacking yields strict upper limits on the HCN/FIR ($\leq$3.6$\times$10$^{-4}$) and HCN/CO(1-0) ratios ($\leq$0.045). The inferred HCN/FIR ratios (a proxy for the star-formation efficiency) are consistent with those in z$\sim$0 FIR-luminous starbursts. However, the HCN/CO ratios - a proxy for the dense-gas fraction - are a factor of a few lower than suggested by the two previous DSFG detections. Our results imply that most DSFGs have low dense-gas fractions. A comparison with Krumholz & Thompson (2007) models of star-forming galaxies indicates that the bulk of gas in DSFGs is at lower densities ($\approx$10$^2$ cm$^{-3}$ ), similar to "normal" star-forming galaxies, rather than ultraluminous starbursts.

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arXiv2022

Tomography of the environment of the COSMOS/AzTEC-3 submillimeter galaxy at z=5.3 revealed by Lyalpha and MUSE observations

We study the members of the protocluster around AzTEC3 submillimeter galaxy at z=5.3. We analyzed the data from the MUSE instrument in an area of 1.4x1.4 arcmin^2 around AzTEC3 and derived information on the Lya line in emission. We compared the Lya profile of various regions of the environment with the zELDA radiative transfer model, revealing the neutral gas distribution and kinematics. We identified 10 Lya emitting sources, including 2 regions with extended emission: one embedding AzTEC3 and LBG3, a star-forming galaxy located 12 kpc north of the SMG and another toward LBG-1, a star-forming galaxy located 90 kpc to the southeast. The sources appear distributed in an elongated configuration of about 70'' in extent. The number of sources confirms the overdensity around AzTEC3. For the AzTEC3+LBG3 system, the Lya emission appears redshifted and more spatially extended than the [CII] line emission. Similarly, the Lya line spectrum is broader in velocity than [CII] for LBG1. In the former spectrum, the Lya emission is elongated to the north of LBG3 and to the south of AzTEC3, where a faint Lya emitting galaxy is also located. The elongated structures could resemble tidal features due to the interaction of the two galaxies with AzTEC3. Also, we find a bridge of gas, revealed by the Lya emission between AzTEC3 and LBG3. The Lya emission toward LBG1 embeds its three components. The HI kinematics support the idea of a merger of the three components. Given the availability of CO and [CII] observations from previous campaigns, and our Lya information, we find evidence of starburst-driven phenomena and interactions around AzTEC-3. The stellar mass of the galaxies of the overdensity and the Lya luminosity of the HI nebula associated with AzTEC-3 imply a dark matter halo of 10^12 Msun at z=5.3 that could evolve into a cluster of 2x10^14 Msun at z=0.

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arXiv2021

MASCOT -- An ESO-ARO legacy survey of molecular gas in nearby SDSS-MaNGA galaxies: I. first data release, and global and resolved relations between H_2 and stellar content

We present the first data release of the MaNGA-ARO Survey of CO Targets (MASCOT), an ESO Public Spectroscopic Survey conducted at the Arizona Radio Observatory (ARO). We measure the CO(1-0) line emission in a sample of 187 nearby galaxies selected from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey that has obtained integral field unit (IFU) spectroscopy for a sample of ~ 10,000 galaxies at low redshift. The main goal of MASCOT is to probe the molecular gas content of star-forming galaxies with stellar masses > 10^9.5 M_solar and with associated MaNGA IFU observations and well-constrained quantities like stellar masses, star formation rates and metallicities. In this paper we present the first results of the MASCOT survey, providing integrated CO(1-0) measurements that cover several effective radii of the galaxy and present CO luminosities, CO kinematics, and estimated H2 gas masses. We observe that the decline of galaxy star formation rate with respect to the star formation main sequence (SFMS) increases with the decrease of molecular gas and with a reduced star formation efficiency, in agreement with results of other integrated studies. Relating the molecular gas mass fractions with the slope of the stellar age gradients inferred from the MaNGA observations, we find that galaxies with lower molecular gas mass fractions tend to show older stellar populations close to the galactic center, while the opposite is true for galaxies with higher molecular gas mass fractions, providing tentative evidence for inside-out quenching.

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arXiv2020

COLDz: Deep 34 GHz Continuum Observations and Free-free Emission in High-redshift Star-forming Galaxies

The high-frequency radio sky has historically remained largely unexplored due to the typical faintness of sources in this regime, and the modest survey speed compared to observations at lower frequencies. However, high-frequency radio surveys present an invaluable tracer of high-redshift star-formation, as they directly target the faint radio free-free emission. We present deep continuum observations at 34 GHz in the COSMOS and GOODS-North fields from the Karl G. Jansky Very Large Array (VLA), as part of the COLDz survey. The deep COSMOS mosaic spans $\sim10\text{arcmin}^2$ down to $\sigma=1.3\mu\text{Jy beam}^{-1}$, while the wider GOODS-N observations cover $\sim50\text{arcmin}^2$ to $\sigma=5.3\mu\text{Jy beam}^{-1}$. We present the deepest 34 GHz radio number counts to date, with five and thirteen continuum detections in COSMOS and GOODS-N, respectively. Nine galaxies show 34 GHz continuum emission that is originating from star-formation, although for two sources this is likely due to thermal emission from dust. Utilizing deep ancillary radio data at 1.4, 3, 5 and 10 GHz, we decompose the spectra of the remaining seven star-forming galaxies into their synchrotron and thermal free-free components, finding typical thermal fractions and synchrotron spectral indices comparable to those observed in local star-forming galaxies. Using calibrations from the literature, we determine free-free star-formation rates (SFRs), and show that these are in agreement with SFRs from spectral energy distribution fitting and the far-infrared/radio correlation. Our observations place strong direct constraints on the high-frequency radio emission in typical galaxies at high-redshift, and provide some of the first insight in what is set to become a key area of study with future radio facilities as the Square Kilometer Array Phase 1 and next-generation VLA.

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arXiv2020

Observations of [OI]63micron line emission in main-sequence galaxies at z~1.5

We present Herschel-PACS spectroscopy of four main-sequence star-forming galaxies at z~1.5. We detect [OI]63micron line emission in BzK-21000 at z=1.5213, and measure a line luminosity, L([OI]63micron) = (3.9+/-0.7)x1.E+9 Lsun. Our PDR modelling of the interstellar medium in BzK-21000 suggests a UV radiation field strength, G~320 G0, and gas density, n~1800 cm-3, consistent with previous LVG modelling of the molecular CO line excitation. The other three targets in our sample are individually undetected in these data, and we perform a spectral stacking analysis which yields a detection of their average emission and an [OI]63micron line luminosity, L([OI]63micron) =(1.1+/-0.2)x1E+9 Lsun. We find that the implied luminosity ratio, L([OI]63micron)/L(IR), of the undetected BzK-selected star-forming galaxies broadly agrees with that of low-redshift star-forming galaxies, while BzK-21000 has a similar ratio to that of a dusty star-forming galaxy at z~6. The high [OI]63micron line luminosities observed in BzK-21000 and the $z \sim 1 -3$ dusty and submm luminous star-forming galaxies may be associated with extended reservoirs of low density, cool neutral gas.

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arXiv2017

Galaxy Formation Through Filamentary Accretion at z=6.1

We present ALMA observations of the dust continuum and [C II] 158um line emission from the z=6.0695 Lyman Break Galaxy WMH5. These observations at 0.3" spatial resolution show a compact (~3kpc) main galaxy in dust and [C II] emission, with a 'tail' of emission extending to the east by about 5kpc (in projection). The [C II] tail is comprised predominantly of two distinct sub-components in velocity, separated from the core by ~100 and 250km/s, with narrow intrinsic widths of about 80km/s, which we call 'sub-galaxies'. The sub-galaxies themselves are extended east-west by about 3kpc in individual channel images. The [C II] tail joins smoothly into the main galaxy velocity field. The [C II] line to continuum ratios are comparable for the main and sub-galaxy positions, within a factor 2. In addition, these ratios are comparable to z~5.5 LBGs. We conjecture that the WMH5 system represents the early formation of a galaxy through the accretion of smaller satellite galaxies, embedded in a smoother gas distribution, along a possibly filamentary structure. The results are consistent with current cosmological simulations of early galaxy formation, and support the idea of very early enrichment with dust and heavy elements of the accreting material.

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arXiv2017

The final data release of ALLSMOG: a survey of CO in typical local low-M* star-forming galaxies

We present the final data release of the APEX low-redshift legacy survey for molecular gas (ALLSMOG), comprising CO(2-1) emission line observations of 88 nearby, low-mass (10^8.5<M* [M_Sun]<10^10) star-forming galaxies carried out with the 230 GHz APEX-1 receiver on the APEX telescope. The main goal of ALLSMOG is to probe the molecular gas content of more typical and lower stellar mass galaxies than have been studied by previous CO surveys. We also present IRAM 30m observations of the CO(1-0) and CO(2-1) emission lines in nine galaxies aimed at increasing the M*<10^9 M_Sun sample size. In this paper we describe the observations, data reduction and analysis methods and we present the final CO spectra together with archival HI 21cm line observations for the entire sample of 97 galaxies. At the sensitivity limit of ALLSMOG, we register a total CO detection rate of 47%. Galaxies with higher M*, SFR, nebular extinction (A_V), gas-phase metallicity (O/H), and HI gas mass have systematically higher CO detection rates. In particular, the parameter according to which CO detections and non-detections show the strongest statistical differences is the gas-phase metallicity, for any of the five metallicity calibrations examined in this work. We investigate scaling relations between the CO(1-0) line luminosity and galaxy-averaged properties using ALLSMOG and a sub-sample of COLD GASS for a total of 185 sources that probe the local main sequence (MS) of star-forming galaxies and its +-0.3 dex intrinsic scatter from M* = 10^8.5 M_Sun to M* = 10^11 M_Sun. L'_{CO(1-0)} is most strongly correlated with the SFR, but the correlation with M* is closer to linear and almost comparably tight. The relation between L'_{CO(1-0)} and metallicity is the steepest one, although deeper CO observations of galaxies with A_V<0.5 mag may reveal an as much steep correlation with A_V. [abridged]

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arXiv2017

Extended ionised and clumpy gas in a normal galaxy at z=7.1 revealed by ALMA

We present new ALMA observations of the [OIII]88$\mu$m line and high angular resolution observations of the [CII]158$\mu$m line in a normal star forming galaxy at z$=$7.1. Previous [CII] observations of this galaxy had detected [CII] emission consistent with the Ly$\alpha$ redshift but spatially slightly offset relative to the optical (UV-rest frame) emission. The new [CII] observations reveal that the [CII] emission is partly clumpy and partly diffuse on scales larger than about 1kpc. [OIII] emission is also detected at high significance, offset relative to the optical counterpart in the same direction as the [CII] clumps, but mostly not overlapping with the bulk of the [CII] emission. The offset between different emission components (optical/UV and different far-IR tracers) is similar to what observed in much more powerful starbursts at high redshift. We show that the [OIII] emitting clump cannot be explained in terms of diffuse gas excited by the UV radiation emitted by the optical galaxy, but it requires excitation by in-situ (slightly dust obscured) star formation, at a rate of about 7 M$_{\odot}$/yr. Within 20 kpc from the optical galaxy the ALMA data reveal two additional [OIII] emitting systems, which must be star forming companions. We discuss that the complex properties revealed by ALMA in the z$\sim$7.1 galaxy are consistent with expectations by recent models and cosmological simulations, in which differential dust extinction, differential excitation and different metal enrichment levels, associated with different subsystems assembling a galaxy, are responsible for the different appearance of the system when observed with different tracers.

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arXiv2016

The Discovery of Gas-Rich, Dusty Starbursts in Luminous Reddened Quasars at $z\sim2.5$ with ALMA

We present ALMA observations of cold dust and molecular gas in four high-luminosity, heavily reddened (A$_{\rm{V}} \sim 2.5-6$ mag) Type 1 quasars at $z\sim2.5$ with virial M$_{\rm{BH}} \sim 10^{10}$M$_\odot$, to test whether dusty, massive quasars represent the evolutionary link between submillimetre bright galaxies (SMGs) and unobscured quasars. All four quasars are detected in both the dust continuum and in the $^{12}$CO(3-2) line. The mean dust mass is 6$\times$10$^{8}$M$_\odot$ assuming a typical high redshift quasar spectral energy distribution (T=41K, $\beta$=1.95 or T=47K, $\beta$=1.6). The implied star formation rates are very high - $\gtrsim$1000 M$_\odot$ yr$^{-1}$ in all cases. Gas masses estimated from the CO line luminosities cover $\sim$1-5$\times10^{10}$($\alpha_{\rm{CO}} / 0.8$)M$_\odot$ and the gas depletion timescales are very short - $\sim5-20$Myr. A range of gas-to-dust ratios is observed in the sample. We resolve the molecular gas in one quasar - ULASJ2315$+$0143 ($z=2.561$) - which shows a strong velocity gradient over $\sim$20 kpc. The velocity field is consistent with a rotationally supported gas disk but other scenarios, e.g. mergers, cannot be ruled out at the current resolution of these data. In another quasar - ULASJ1234+0907 ($z=2.503$) - we detected molecular line emission from two millimetre bright galaxies within 200 kpc of the quasar, suggesting that this quasar resides in a significant over-density. The high detection rate of both cold dust and molecular gas in these sources, suggests that reddened quasars could correspond to an early phase in massive galaxy formation associated with large gas reservoirs and significant star formation.

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arXiv2016

New Constraints on the Molecular Gas in the Prototypical HyLIRGs BRI1202-0725 & BRI1335-0417

We present Karl G Jansky Very Large Array (VLA) observations of CO(2-1) line emission and rest-frame 250GHz continuum emission of the Hyper-Luminous IR Galaxies (HyLIRGs) BRI1202-0725 (z=4.69) and BRI1335-0417 (z=4.41), with an angular resolution as high as 0.15". Our low order CO observations delineate the cool molecular gas, the fuel for star formation in the systems, in unprecedented detail. For BRI1202-0725, line emission is seen from both extreme starburst galaxies: the quasar host and the optically obscured submm galaxy (SMG), in addition to one of the Lyman-alpha emitting galaxies in the group. Line emission from the SMG shows an east-west extension of about 0.6". For Lyalpha-2, the CO emission is detected at the same velocity as [CII] and [NII], indicating a total gas mass ~4.0*10^10 solar masses. The CO emission from BRI1335-0417 peaks at the nominal quasar position, with a prominent northern extension (~1", a possible tidal feature). The gas depletion timescales are ~10^7 years for the three HyLIRGs, consistent with extreme starbursts, while that of Lyalpha-2 may be consistent with main sequence galaxies. We interpret these sources as major star formation episodes in the formation of massive galaxies and supermassive black holes (SMBHs) via gas rich mergers in the early Universe.

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arXiv2016

ALMA spectroscopic survey in the Hubble Ultra Deep Field: Continuum number counts, resolved 1.2-mm extragalactic background, and properties of the faintest dusty star forming galaxies

We present an analysis of a deep (1$\sigma$=13 $\mu$Jy) cosmological 1.2-mm continuum map based on ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field. In the 1 arcmin$^2$ covered by ASPECS we detect nine sources at $>3.5\sigma$ significance at 1.2-mm. Our ALMA--selected sample has a median redshift of $z=1.6\pm0.4$, with only one galaxy detected at z$>$2 within the survey area. This value is significantly lower than that found in millimeter samples selected at a higher flux density cut-off and similar frequencies. Most galaxies have specific star formation rates similar to that of main sequence galaxies at the same epoch, and we find median values of stellar mass and star formation rates of $4.0\times10^{10}\ M_\odot$ and $\sim40~M_\odot$ yr$^{-1}$, respectively. Using the dust emission as a tracer for the ISM mass, we derive depletion times that are typically longer than 300 Myr, and we find molecular gas fractions ranging from $\sim$0.1 to 1.0. As noted by previous studies, these values are lower than using CO--based ISM estimates by a factor $\sim$2. The 1\,mm number counts (corrected for fidelity and completeness) are in agreement with previous studies that were typically restricted to brighter sources. With our individual detections only, we recover $55\pm4\%$ of the extragalactic background light (EBL) at 1.2 mm measured by the Planck satellite, and we recover $80\pm7\%$ of this EBL if we include the bright end of the number counts and additional detections from stacking. The stacked contribution is dominated by galaxies at $z\sim1-2$, with stellar masses of (1-3)$\times$10$^{10}$ M$_\odot$. For the first time, we are able to characterize the population of galaxies that dominate the EBL at 1.2 mm.

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arXiv2016

ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Search for [CII] line and dust emission in 6<z<8 galaxies

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 $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 $S_{1.2mm}=14\pm5\mu$Jy. This implies a dust-obscured star formation rate (SFR) of $(3\pm1)$ 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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arXiv2016

ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: implications for spectral line intensity mapping at millimeter wavelengths and CMB spectral distortions

We present direct estimates of the mean sky brightness temperature in observing bands around 99GHz and 242GHz due to line emission from distant galaxies. These values are calculated from the summed line emission observed in a blind, deep survey for specrtal line emission from high redshift galaxies using ALMA (the 'ASPECS' survey). In the 99 GHz band, the mean brightness will be dominated by rotational transitions of CO from intermediate and high redshift galaxies. In the 242GHz band, the emission could be a combination of higher order CO lines, and possibly [CII] 158$\mu$m line emission from very high redshift galaxies ($z \sim 6$ to 7). The mean line surface brightness is a quantity that is relevant to measurements of spectral distortions of the cosmic microwave background, and as a potential tool for studying large-scale structures in the early Universe using intensity mapping. While the cosmic volume and the number of detections are admittedly small, this pilot survey provides a direct measure of the mean line surface brightness, independent of conversion factors, excitation, or other galaxy formation model assumptions. The mean surface brightness in the 99GHZ band is: $T_B = 0.94\pm 0.09$ $\mu$K. In the 242GHz band, the mean brightness is: $T_B = 0.55\pm 0.033$ $\mu$K. These should be interpreted as lower limits on the average sky signal, since we only include lines detected individually in the blind survey, while in a low resolution intensity mapping experiment, there will also be the summed contribution from lower luminosity galaxies that cannot be detected individually in the current blind survey.

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arXiv2016

Galaxy metallicities depend primarily on stellar mass and molecular gas mass

In this work we present an analysis of the behaviour of galaxies in a four-dimensional parameter space defined by stellar mass, metallicity, star formation rate, and molecular gas mass. We analyse a combined sample of 227 galaxies, which draws from a number of surveys across the redshift range 0 < z < 2 (> 90% of the sample at z~0), and covers > 3 decades in stellar mass.Using Principle Component Analysis, we demonstrate that galaxies in our sample lie on a 2-dimensional plane within this 4D parameter space, indicative of galaxies that exist in an equilibrium between gas inflow and outflow. Furthermore, we find that the metallicity of galaxies depends only on stellar mass and molecular gas mass. In other words, gas-phase metallicity has a negligible dependence on star formation rate, once the correlated effect of molecular gas content is accounted for. The well-known `fundamental metallicity relation', which describes a close and tight relationship between metallicity and SFR (at fixed stellar mass) is therefore entirely a by-product of the underlying physical relationship with molecular gas mass (via the Schmidt-Kennicutt relation).

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arXiv2016

The Science Case for ALMA Band 2 and Band 2+3

We discuss the science drivers for ALMA Band 2 which spans the frequency range from 67 to 90 GHz. The key science in this frequency range are the study of the deuterated molecules in cold, dense, quiescent gas and the study of redshifted emission from galaxies in CO and other species. However, Band 2 has a range of other applications which are also presented. The science enabled by a single receiver system which would combine ALMA Bands 2 and 3 covering the frequency range 67 to 116 GHz, as well as the possible doubling of the IF bandwidth of ALMA to 16 GHz, are also considered.

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arXiv2016

First observational support for overlapping reionized bubbles generated by a galaxy overdensity

We present the analysis of deep HST multi-band imaging of the BDF field specifically designed to identify faint companions around two of the few Ly-alpha emitting galaxies spectroscopically confirmed at z~7 (Vanzella et al. 2011). Although separated by only 4.4 proper Mpc these galaxies cannot generate HII regions large enough to explain visibility of their Ly-alpha line, thus requiring a population of fainter ionizing sources in their vicinity. We use deep HST and VLT-Hawk-I data to select z~7 Lyman break galaxies around the emitters. We select 6 new robust z~7 LBGs at Y~26.5-27.5 whose average spectral energy distribution is consistent with the objects being at the redshift of the close-by Ly-alpha emitters. The resulting number density of z~7 LBGs in the BDF field is a factor ~3-4 higher than expected in random pointings of the same size. We compare these findings with cosmological hydrodynamic plus radiative transfer simulations of a universe with a half neutral IGM: we find that indeed Ly-alpha emitter pairs are only found in completely ionized regions characterized by significant LBG overdensities. Our findings match the theoretical prediction that the first ionization fronts are generated within significant galaxy overdensities and support a scenario where faint, "normal" star-forming galaxies are responsible for reionization.

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