Galaxy formation and evolution

Abstract:

ABSTRACT We introduce the ‘Engineering Dwarfs at Galaxy Formation’s Edge’ (EDGE) project to study the cosmological formation and evolution of the smallest galaxies in the Universe. In this first paper, we explore the effects of resolution and sub-grid physics on a single low-mass halo ($M_{\rm halo}=10^{9}{\, \rm M}_\odot$), simulated to redshift z = 0 at a mass and spatial resolution of $\sim 20{\, \rm M}_\odot$ and ∼3 pc. We consider different star formation prescriptions, supernova feedback strengths, and on-the-fly radiative transfer (RT). We show that RT changes the mode of galactic self-regulation at this halo mass, suppressing star formation by causing the interstellar and circumgalactic gas to remain predominantly warm (∼104 K) even before cosmic reionization. By contrast, without RT, star formation regulation occurs only through starbursts and their associated vigorous galactic outflows. In spite of this difference, the entire simulation suite (with the exception of models without any feedback) matches observed dwarf galaxy sizes, velocity dispersions, V-band magnitudes, and dynamical mass-to-light-ratios. This is because such structural scaling relations are predominantly set by the host dark matter halo, with the remaining model-to-model variation being smaller than the observational scatter. We find that only the stellar mass–metallicity relation differentiates the galaxy formation models. Explosive feedback ejects more metals from the dwarf, leading to a lower metallicity at a fixed stellar mass. We conclude that the stellar mass–metallicity relation of the very smallest galaxies provides a unique constraint on galaxy formation physics.

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 present the confusion-limited 1.28 GHz MeerKAT DEEP2 image covering one $\approx 68'$ FWHM primary beam area with $7.6''$ FWHM resolution and $0.55 \pm 0.01$ $\mu$Jy/beam rms noise. Its J2000 center position $\alpha=04^h 13^m 26.4^s$, $\delta=-80^\circ 00' 00''$ was selected to minimize artifacts caused by bright sources. We introduce the new 64-element MeerKAT array and describe commissioning observations to measure the primary beam attenuation pattern, estimate telescope pointing errors, and pinpoint $(u,v)$ coordinate errors caused by offsets in frequency or time. We constructed a 1.4 GHz differential source count by combining a power-law count fit to the DEEP2 confusion $P(D)$ distribution from $0.25$ to $10$ $\mu$Jy with counts of individual DEEP2 sources between $10$ $\mu$Jy and $2.5$ mJy. Most sources fainter than $S \sim 100$ $\mu$Jy are distant star-forming galaxies obeying the FIR/radio correlation, and sources stronger than $0.25$ $\mu$Jy account for $\sim93\%$ of the radio background produced by star-forming galaxies. For the first time, the DEEP2 source count has reached the depth needed to reveal the majority of the star formation history of the universe. A pure luminosity evolution of the 1.4 GHz local luminosity function consistent with the Madau & Dickinson (2014) model for the evolution of star-forming galaxies based on UV and infrared data underpredicts our 1.4 GHz source count in the range $-5 \lesssim \log[S(\mathrm{Jy})] \lesssim -4$.

Abstract:

HARMONI is the first light visible and near-infrared (NIR) integral field spectrograph for the Extremely Large Telescope(ELT). The HARMONI spectrograph will have four near-infrared cameras and two visible, both with seven lenses of various materials and diameters ranging from 286 to 152 mm. The lens mounts design has been optimized for each lens material to compensate for thermal stresses and maintain lens alignment at the operational temperature of 130 K. We discuss their design and mounting concept, as well as assembly and verification steps. We show initial results from two prototypes and outline improvements in the mounting procedures to reach tighter lens alignments. To conclude, we present a description of our future work to measure the decentering of the lenses when cooled down and settled.