Plateau de Bure High-z Blue Sequence Survey 2 (PHIBSS2): Search for Secondary Sources, CO Luminosity Functions in the Field, and the Evolution of Molecular Gas Density through Cosmic Time*

Abstract

We report on the results of a search for serendipitous sources in CO emission in 110 cubes targeting CO (2 − 1), CO (3 − 2), and CO (6 − 5) at z ∼ 1 − 2 from the second Plateau de Bure High-z Blue-Sequence Survey (PHIBSS2). The PHIBSS2 observations were part of a 4-year legacy program at the IRAM Plateau de Bure Interferometer aimed at studying early galaxy evolution from the perspective of molecular gas reservoirs. We present a catalog of 67 candidate secondary sources from this search, with 45 out of the 110 data cubes showing sources in addition to the primary target that appear to be field detections, unrelated to the central sources. This catalog includes the redshifts, line widths, fluxes, as well as an estimation of their reliability based on their false positive probability. We perform a search in the 3D-HST/CANDELS catalogs for the secondary CO detections and tentatively find that ∼ 64% of these have optical counterparts, which we use to constrain their redshifts. Finally, we use our catalog of candidate CO detections to derive the CO (2 − 1), CO (3 − 2), CO (4 − 3), CO (5 − 4), and CO (6 − 5) luminosity functions over a range of redshifts, as well as the molecular gas mass density evolution. Despite the different methodology, these results are in very good agreement with previous observational constraints derived from blind searches in deep fields. They provide an example of the type of "deep field" science that can be carried out with targeted observations.

VLA–ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (VLASPECS): Total Cold Gas Masses and CO Line Ratios for z = 2–3 Main-sequence Galaxies

“…31 The formal 1σ range is log( ( ) r H 2 /M e Mpc −3 )=7.20-7.63. 32 Given the focus of this work, we here restrict the comparison to results from blank-field CO surveys, and defer comparisons to results from other methods (e.g., Scoville et al 2017;Liu et al 2019;Lenkić et al 2020) to a future publication (R. Decarli et al 2020, in preparation), but we note that the results from these studies are broadly consistent with those presented here. 33 These findings assume that the α CO conversion factor for the galaxy populations dominating the signal does not change significantly with redshift, which is consistent with our current constraints.…”

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Multiband Constraints on Line-luminosity Functions and the Cosmic Density of Molecular Gas

“…In Figure 9 we place the ASPECS measures of ρ H2 (z) in the context of similar investigations in the literature. Our new measurements, listed in Table 2, improve and expand on the results from previous molecular scans using the Plateau de Bure Interferometer (Walter et al 2014), the VLA (Riechers et al 2019), and ALMA (Decarli et al 2016a(Decarli et al , 2019, as well as the constraints from field sources in the PHIBSS data (Lenkić et al 2020), and from calibrator fields in the ALMACAL survey (Klitsch et al 2019). Our comparison also includes dust-based ρ H2 (z) measurements from Scoville et al (2017); Liu et al (2019), and from ASPECS (Magnelli et al 2020).…”

“…Other molecular scan efforts in the literature are as follows: the COLDz survey used >320 hr of the VLA time to sample CO(1-0) emission at z≈2-3 ("cosmic noon") as well as CO(2-1) at z≈5−7 over ∼60 arcmin 2 in parts of the COSMOS (Scoville et al 2007) and GOODS-North (Giavalisco et al 2004) fields (Pavesi et al 2018;Riechers et al 2019. Lenkić et al (2020) used the Plateau de Bure High-z Blue-Sequence Survey 2 (PHIBSS2) data (Tacconi et al 2018) to search for serendipitous emission in the cubes, in addition the central targets. These studies placed the first direct constraints on the CO luminosity function in galaxies at z∼2, and revealed a higher molecular content in galaxies at these redshifts compared to the local universe: ρ H2 (z=2-3)≈ (1-20)×10 7 M e Mpc −3 .…”

The Evolution of the Star-Forming Interstellar Medium Across Cosmic Time

“…Several sets of authors have taken this blind approach in GOODS-N (DeCarli et al 2014; z = 1.5, 2.5) with NOEMA, in HUDF (DeCarli et al 2016; ASPECS, z = 1, 2.3) with ALMA, and in GOODS-N and COSMOS (Riechers et al 2019; COLDz, z = 2.5, 6) with the JVLA. Most recently, Lenkic et al (2020) analyzed the 110 data cubes of the NOEMA PHIBSS2 pointed CO survey (Tacconi et al 2018, Freundlich et al 2019) of z ∼ 0.5-2.5 MS SFGs to search for additional serendipitous sources Davé et al 2017 Popping et al 2019Popping et al 2019Obreschkow et al 2009Lagos et al 2011Popping et al 2014Lagos et al 2015 This review Different observational and theoretical estimates of the cosmic evolution of total molecular mass (H 2 plus helium) density per comoving volume. The different boxes denote estimates at different redshifts with the deep field technique (DeCarli et al 2014(DeCarli et al , 2016Aravena et al 2016;Riechers et al 2019).…”

“…The gray-shaded boxes show the serendipitous detections of secondary sources in the same data cubes as those from the pointed PHIBSS2@NOEMA survey, which is another way to construct a blind survey (Lenkic et al 2020). The PHIBSS2 survey covers a larger cosmic volume than the other blind surveys, yielding smaller uncertainties.…”