Rubin-LSST

Abstract:

We present the radio luminosity function (RLF) of optically selected quasars below 1 mJy, constructed by applying a Bayesian-fitting stacking technique to objects well below the nominal radio flux density limit. We test the technique using simulated data, confirming that we can reconstruct the RLF over three orders of magnitude below the typical 5σ detection threshold. We apply our method to 1.4-GHz flux densities from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey, extracted at the positions of optical quasars from the Sloan Digital Sky Survey over seven redshift bins up to z = 2.15, and measure the RLF down to two orders of magnitude below the FIRST detection threshold. In the lowest redshift bin (0.2 < z < 0.45), we find that our measured RLF agrees well with deeper data from the literature. The RLF for the radio-loud quasars flattens below log10[L1.4/WHz−1]≈25.5 and becomes steeper again below log10[L1.4/WHz−1]≈24.8⁠, where radio-quiet quasars start to emerge. The radio luminosity where radio-quiet quasars emerge coincides with the luminosity where star-forming galaxies are expected to start dominating the radio source counts. This implies that there could be a significant contribution from star formation in the host galaxies, but additional data are required to investigate this further. The higher redshift bins show a similar behaviour to the lowest z bin, implying that the same physical process may be responsible.

Abstract:

Aims: Our aim is to search for and characterize inflows and outflows of molecular gas in four ultraluminous infrared galaxies (ULIRGs; LIR >  1012L⊙) at z ∼ 0.2−0.3 and one distant quasi-stellar object (QSO) at z = 6.13.

Methods: We used Herschel/PACS and ALMA Band 7 observations of the hydroxyl molecule (OH) line at rest-frame wavelength 119 μm, which in absorption can provide unambiguous evidence of inflows or outflows of molecular gas in nuclear regions of galaxies. Our study contributes to doubling the number of OH 119 μm observations of luminous systems at z ∼ 0.2−0.3, and pushes the search for molecular outflows based on the OH 119 μm transition to z ∼ 6.

Results: We detect OH 119 μm high-velocity absorption wings in three of the four ULIRGs. In two cases, IRAS F20036−1547 and IRAS F13352+6402, the blueshifted absorption profiles indicate the presence of powerful and fast (∼200−500 km s−1) molecular gas outflows. Consistent with an inside-out quenching scenario, these outflows are depleting the central reservoir of star-forming molecular gas at a rate similar to that of intense star formation activity. For the starburst-dominated system IRAS 10091+4704, we detect an inverted P Cygni profile that is unique among ULIRGs and indicates the presence of a fast (∼400 km s−1) inflow of molecular gas at a rate of ∼100 M⊙ yr−1 towards the central region. Finally, we tentatively detect (∼3σ) the OH 119 μm doublet in absorption in the z = 6.13 QSO ULAS J131911+095051. The OH 119 μm feature is blueshifted with a median velocity that suggests the presence of a molecular outflow, although characterized by a modest molecular mass loss rate of ∼200 M⊙ yr−1. This value is comparable to the small mass outflow rates found in the stacking of the [C II] spectra of other z ∼ 6 QSOs and suggests that ejective feedback in this phase of the evolution of ULAS J131911+095051 has subsided.

Abstract:

We investigate one-halo galactic conformity (the tendency for satellite galaxies to mirror the properties of their central) in both star formation and morphology using a sample of 8230 galaxies in 1266 groups with photometry and spectroscopy from the Sloan Digital Sky Survey, morphologies from Galaxy Zoo and group memberships as determined by Yang et al. This is the first paper to investigate galactic conformity in both star formation and visual morphology properties separately. We find that the signal of galactic conformity is present at low significance in both star formation and visual morphological properties, however it is stronger in star formation properties. Over the entire halo mass range we find that groups with star-forming (spiral) centrals have, on average, a fraction 0.18 ± 0.08 (0.08 ± 0.06) more star-forming (spiral) satellites than groups with passive (early-type) centrals at a similar halo mass. We also consider conformity in groups with four types of central: passive early-types, star-forming spirals, passive spirals, and star-forming early-types (which are very rarely centrals), finding that the signal of morphological conformity is strongest around passive centrals regardless of morphology; although blue spiral centrals are also more likely than average to have blue spiral satellites. We interpret these observations of the relative size of the conformity signal as supporting a scenario where star formation properties are relatively easily changed, while morphology changes less often/more slowly for galaxies in the group environment.