NGC 253 hosts the nearest nuclear starburst. Previous observations show a region rich in molecular gas, with dense clouds associated with recent star formation. We used ALMA to image the 350 GHz dust continuum and molecular line emission from this region at 2 pc resolution. Our observations reveal ∼ 14 bright, compact (∼ 2−3 pc FWHM) knots of dust emission. Most of these sources are likely to be forming super star clusters (SSCs) based on their inferred dynamical and gas masses, association with 36 GHz radio continuum emission, and coincidence with line emission tracing dense, excited gas. One source coincides with a known SSC, but the rest remain invisible in Hubble near-infrared (IR) imaging. Our observations imply that gas still constitutes a large fraction of the overall mass in these sources. Their high brightness temperature at 350 GHz also implies a large optical depth near the peak of the IR spectral energy distribution. As a result, these sources may have large IR photospheres and the IR radiation force likely exceeds L/c. Still, their moderate observed velocity dispersions suggest that feedback from radiation, winds, and supernovae are not yet disrupting most sources. This mode of star formation appears to produce a large fraction of stars in the burst. We argue for a scenario in which this phase lasts ∼ 1 Myr, after which the clusters shed their natal cocoons but continue to produce ionizing photons. The strong feedback that drives the observed cold gas and X-ray outflows likely occurs after the clusters emerge from this early phase.

We present 0.15 (∼ 2.5 pc) resolution ALMA CO(3-2) observations of the starbursting center in NGC 253. Together with archival ALMA CO(1-0) and CO(2-1) data we decompose the emission into a disk and non-disk component. We find ∼ 7 − 16% of the CO luminosity to be associated with the non-disk component (1.2 − 4.2 × 10 7 K km s −1 pc 2 ). The total molecular gas mass in the center of NGC 253 is ∼ 3.6 × 10 8 M with ∼ 0.5 × 10 8 M (∼ 15%) in the non-disk component. These measurements are consistent across independent mass estimates through three CO transitions. The high-resolution CO(3-2) observations allow us to identify the molecular outflow within the non-disk gas. Using a starburst conversion factor, we estimate the deprojected molecular mass outflow rate, kinetic energy and momentum in the starburst of NGC 253. The deprojected molecular mass outflow rate is in the range ∼ 14 − 39 M yr −1 with an uncertainty of 0.4 dex. The large spread arises due to different interpretations of the kinematics of the observed gas while the errors are due to unknown geometry. The majority of this outflow rate is contributed by distinct outflows perpendicular to the disk, with a significant contribution by diffuse molecular gas. This results in a mass loading factor η =Ṁ out /Ṁ SFR in the range η ∼ 8 − 20 for gas ejected out to ∼ 300 pc. We find the kinetic energy of the outflow to be ∼ 2.5 − 4.5 × 10 54 erg and ∼ 0.8 dex typical error which is ∼ 0.1% of the total or ∼ 8% of the kinetic energy supplied by the starburst. The outflow momentum is 4.8 − 8.7 × 10 8 M km s −1 (∼ 0.5 dex error) or ∼ 2.5 − 4% of the kinetic momentum released into the ISM by feedback. The unknown outflow geometry and launching sites are the primary source of uncertainty in this study.

We present Karl G Jansky Very Large Array molecular line observations of the nearby starburst galaxy NGC 253, from SWAN: "Survey of Water and Ammonia in Nearby galaxies". SWAN is a molecular line survey at centimeter wavelengths designed to reveal the physical conditions of star forming gas over a range of star forming galaxies. NGC 253 has been observed in four 1GHz bands from 21 to 36 GHz at 6 ∼ 100 pc) spatial and 3.5 km s −1 spectral resolution. In total we detect 19 transitions from seven molecular and atomic species. We have targeted the metastable inversion transitions of ammonia (NH 3 ) from (1,1) to (5,5) and the (9,9) line, the 22.2 GHz water (H 2 O) (6 16 − 5 23 ) maser, and the 36.1 GHz methanol (CH 3 OH) (4 −1 − 3 0 ) maser. Utilizing NH 3 as a thermometer, we present evidence for uniform heating over the central kpc of NGC 253. The molecular gas is best described by a two kinetic temperature model with a warm 130K and a cooler 57K component. A comparison of these observations with previous ALMA results suggests that the molecular gas is not heated in photon dominated regions or shocks. It is possible that the gas is heated by turbulence or cosmic rays. In the galaxy center we find evidence for NH 3 (3,3) masers. Furthermore we present velocities and luminosities of three water maser features related to the nuclear starburst. We partially resolve CH 3 OH masers seen at the edges of the bright molecular emission, which coincides with expanding molecular superbubbles. This suggests that the masers are pumped by weak shocks in the bubble surfaces.

We measured the X-ray fluxes from an optically-selected sample of blue compact dwarf galaxies (BCDs) with metallicities <0.07 and solar distances less than 15 Mpc. Four X-ray point sources were observed in three galaxies, with five galaxies having no detectable X-ray emission. Comparing X-ray luminosity and star formation rate, we find that the total X-ray luminosity of the sample is more than 10 times greater than expected if X-ray luminosity scales with star formation rate according to the relation found for normal-metallicity star-forming galaxies. However, due to the low number of sources detected, one can exclude the hypothesis that the relation of the X-ray binaries to SFR in low-metalicity BCDs is identical to that in normal galaxies only at the 96.6% confidence level. It has recently been proposed that X-ray binaries were an important source of heating and reionization of the intergalactic medium at the epoch of reionization. If BCDs are analogs to unevolved galaxies in the early universe, then enhanced X-ray binary production in BCDs would suggest an enhanced impact of X-ray binaries on the early thermal history of the universe.