The Lockman Hole project: gas and galaxy properties from a stacking experiment

Geréb, K.; Morganti, Raffaella; Oosterloo, Tom; Guglielmino, G.; Prandoni, I.

doi:10.1051/0004-6361/201322113

Cited by 24 publications

(36 citation statements)

References 41 publications

(54 reference statements)

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“…In a previous paper (Geréb et al 2013, i.e. Paper I) we carried out spectral stacking on galaxies selected in the Lockman Hole (LH) field.…”

Section: Introductionmentioning

confidence: 88%

“…Stacking is done similarly as described in Geréb et al (2013), centred on the redshift of the galaxy to be stacked. Galaxies are stacked in four redshift ranges, between 0.02 < z < 0.12 each redshift range covers Δz = 0.02 (except the highest redshift range, 0.08 < z < 0.12).…”

Section: Data Reduction and H I Stackingmentioning

confidence: 99%

“…Previous stacking studies, including our LH analysis, were carried out on galaxies separated into blue/red samples, which colors were defined based on ultraviolet-optical NUV − r, or optical g − r selections (Fabello et al 2011a;Geréb et al 2013). To expand on previous studies, in this paper we consider the green valley as a separate population.…”

Section: Data Reduction and H I Stackingmentioning

confidence: 99%

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From star-forming galaxies to AGN: the global HI content from a stacking experiment

Geréb

Morganti

Oosterloo

et al. 2015

A&A

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We study the atomic neutral hydrogen (H I) content of ∼1600 galaxies up to z ∼ 0.1 using stacking techniques. The observations were carried out with the Westerbork Synthesis Radio Telescope (WSRT) in the area of the SDSS South Galactic Cap (SSGC), where we selected a galaxy sample from the SDSS spectroscopic catalog. Multi-wavelength information is provided by SDSS, NVSS, GALEX, and WISE. We use the collected information to study H I trends with color, star-forming, and active galactic nuclei (AGN) properties. Using near-UV (NUV) − r colors, galaxies are divided into blue cloud, green valley and red sequence galaxies. As expected based on previous observations, we detect H I in green valley objects with lower amounts of H I than blue galaxies, while stacking only produces a 3σ upper limit for red galaxies with M HI < (5 ± 1.5) × 10 8 M and M HI /L r < 0.02 ± 0.006 M /L (averaged over four redshift bins up to z ∼ 0.1). We find that the H I content is more dependent on NUV − r color, and less on ionization properties, in the sense that regardless of the presence of an optical AGN (based on optical ionization line diagnostics), green-valley galaxies always show H I, whereas red galaxies only produce an upper limit. This suggests that feedback from optical AGN is not the (main) reason for depleting large-scale gas reservoirs. Low-level radio continuum emission in our galaxies can stem either from star formation, or from AGN. We use the WISE color-color plot to separate these phenomena by dividing the sample into IR late-type and IR early-type galaxies. We find that the radio emission in IR late-type galaxies stems from enhanced star formation, and this group is detected in H I. However, IR early-type galaxies lack any sign of H I gas and star formation activity, suggesting that radio AGN are likely to be the source of radio emission in this population. Future H I surveys will allow for extending our studies to higher redshift, and for testing any possible evolution of the H I content in relation to star-forming and AGN properties up to cosmologically significant distances. Such surveys will provide enough data to test the effect of radio/optical AGN feedback on the H I content at lower, currently rather unexplored H I detection limit (M HI < 10 7 M ).

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“…In a previous paper (Geréb et al 2013, i.e. Paper I) we carried out spectral stacking on galaxies selected in the Lockman Hole (LH) field.…”

Section: Introductionmentioning

confidence: 88%

Section: Data Reduction and H I Stackingmentioning

confidence: 99%

Section: Data Reduction and H I Stackingmentioning

confidence: 99%

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From star-forming galaxies to AGN: the global HI content from a stacking experiment

Geréb

Morganti

Oosterloo

et al. 2015

A&A

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“…We adapted the script used for H i emission studies in Geréb et al (2013) to perform stacking of H i absorption. The spectra are extracted at the peak of the continuum source, assuming that the sources are unresolved.…”

Section: H I Stacking: Testing the H I Distribution Of Agn Down To Lomentioning

confidence: 99%

Probing the gas content of radio galaxies through H I absorption stacking

Geréb

Morganti

Oosterloo

2014

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Using the Westerbork Synthesis Radio Telescope, we carried out shallow H i absorption observations of a flux-selected (S 1.4 GHz > 50 mJy) sample of 93 radio active galactic nuclei (AGN), which have available SDSS (Sloan Digital Sky Survey) redshifts between 0.02 < z < 0.23. Our main goal is to study the gas properties of radio sources down to S 1.4 GHz flux densities not systematically explored before using, for the first time, stacking of absorption spectra of extragalactic H i. Despite the shallow observations, we obtained a direct detection rate of ∼29%, comparable with deeper studies of radio galaxies. Furthermore, detections are found at every S 1.4 GHz flux level, showing that H i absorption detections are not biased toward brighter sources. The stacked profiles of detections and non-detections reveal a clear dichotomy in the presence of H i, with the 27 detections showing an average peak τ = 0.02 corresponding to N(H i) ∼ (7.4 ± 0.2) × 10 18 (T spin /c f ) cm −2 , while the 66 non-detections remain undetected upon stacking with a peak optical depth upper limit τ < 0.002 corresponding to N(H i) < (2.26 ± 0.06) × 10 17 (T spin /c f ) cm −2 (using a FWHM of 62 km s −1 , derived from the mean width of the detections). Separating the sample into compact and extended radio sources increases the detection rate, optical depth, and FWHM for the compact sample. The dichotomy for the stacked profiles of detections and non-detections still holds between these two groups of objects. We argue that orientation effects connected to a disk-like distribution of the H i can be partly responsible for the dichotomy that we see in our sample. However, orientation effects alone cannot explain all the observational results, and some of our galaxies must be genuinely depleted of cold gas. A fraction of the compact sources in the sample are confirmed by previous studies as likely young radio sources (compact steep spectrum and gigahertz peaked spectrum sources). These show an even higher detection rate of 55%. Along with their high integrated optical depth and wider profile, this reinforces the idea that young radio AGN are embedded in a medium that is rich in atomic gas. Part of our motivation is to probe for the presence of faint H i outflows at low optical depth using stacking. However, the stacked profiles do not reveal any significant blueshifted wing. We are currently collecting more data to investigate the presence of outflows. The results presented in this paper are particularly relevant for future surveys in two ways. The lack of bias toward bright sources is encouraging for the search for H i in sources with even lower radio fluxes planned by such surveys. The results also represent a reference point when searching for H i absorption at higher redshifts.

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“…Stacking has become a common tool to constrain the statistical properties of a population of objects that lack individual detections in a survey, and has been applied to a variety of different astrophysical data, including H I -line spectra (Chengalur et al (2001) Geréb et al (2013)). This technique requires independent measurements of the redshifts of the galaxies, and yields an estimate of the average H I content of a sample of galaxies by co-adding their line emission (see description in Fabello et al (2011)).…”

Section: Pos(aaska14)128mentioning

confidence: 99%

Exploring Neutral Hydrogen and Galaxy Evolution with the SKA

Blyth¹,

Hulst²,

Verheijen³

et al. 2015

Proceedings of Advancing Astrophysics With the Square Kilometre Array — PoS(AASKA14)

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One of the key science drivers for the development of the SKA is to observe the neutral hydrogen, H I , in galaxies as a means to probe galaxy evolution across a range of environments over cosmic time. Over the past decade, much progress has been made in theoretical simulations and observations of H I in galaxies. However, recent H I surveys on both single dish radio telescopes and interferometers, while providing detailed information on global H I properties, the dark matter distribution in galaxies, as well as insight into the relationship between star formation and the interstellar medium, have been limited to the local universe. Ongoing and upcoming H I surveys on SKA pathfinder instruments will extend these measurements beyond the local universe to intermediate redshifts. We present here an overview of the H I science which will be possible with the the SKA and which will build upon the expected increase in knowledge of H I in and around galaxies obtained with the SKA pathfinder surveys. With the SKA1 the greatest improvement is the capability to image galaxies at reasonable linear resolution and good column density sensitivity to much higer redshifts (0.2 < z < 1.7). So one will not only be able to increase the number of detections to study the evolution of the H I mass function, but also have the sensitivity and resolution to study inflows and outflows to and from galaxies and the kinematics of the gas within and around galaxies as a function of environment and cosmic time out to previously unexplored depths. The increased sensitivity of SKA2 will allow us to image Milky Way-size galaxies out to redshifts of z = 1 and will provide the data required for a comprehensive picture of the H I content of galaxies back to z ∼ 2 when the cosmic star formation rate density was at its peak.Advancing Astrophysics with the Square Kilometre Array

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The Lockman Hole project: gas and galaxy properties from a stacking experiment

Cited by 24 publications

References 41 publications

From star-forming galaxies to AGN: the global HI content from a stacking experiment

From star-forming galaxies to AGN: the global HI content from a stacking experiment

Probing the gas content of radio galaxies through H I absorption stacking

Exploring Neutral Hydrogen and Galaxy Evolution with the SKA

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