The H alpha equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic, bursty star-formation activity. Previous assessments show that the H alpha EW strongly anticorrelates with stellar mass as M-0.25 similar to the sSFR - stellar mass relation. However, such a correlation could be driven or even formed by selection effects. In this study, we investigate how H alpha EW distributions correlate with physical properties of galaxies and how selection biases could alter such correlations using a z = 0.47 narrow-band-selected sample of 1572 H alpha emitters from the Ly alpha Galaxies in the Epoch of Reionization (LAGER) survey as our observational case study. The sample covers a 3 deg(2) area of COSMOS with a survey comoving volume of 1.1 x 10(5) Mpc(3). We assume an intrinsic EW distribution to form mock samples of H alpha emitters and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying results. We find that H alpha EW intrinsically correlates with stellar mass as W-0 proportional to M-0.16 +/- 0.03 and decreases by a factor of similar to 3 from 10(7) M-circle dot to 10(10) M-circle dot, while not correcting for selection effects steepens the correlation as M-025 +/- 0.04, We find low-mass H alpha emitters to be similar to 320 times more likely to have rest-frame EW > 200 angstrom compared to high-mass H alpha emitters. Combining the intrinsic W-0-stellar mass correlation with an observed stellar mass function correctly reproduces the observed H alpha luminosity function, while not correcting for selection effects underestimates the number of bright emitters. This suggests that the W-0-stellar mass correlation when corrected for selection effects is physically significant and reproduces three statistical distributions of galaxy populations (line luminosity function, stellar mass function, EW distribution). At lower stellar masses, we find there are more high-EW outliers compared to high stellar masses, even after we take into account selection effects. Our results suggest that high sSFR outliers indicative of bursty star formation activity are intrinsically more prevalent in low-mass H alpha emitters and not a byproduct of selection effects.

Spatially extended halos of H i Ly alpha emission are now ubiquitously found around high-redshift star-forming galaxies. But our understanding of the nature and powering mechanisms of these halos is still hampered by the complex radiative transfer effects of the Ly alpha line and limited angular resolution. In this paper, we present resolved Multi Unit Spectroscopic Explorer (MUSE) observations of SGAS J122651.3+215220, a strongly lensed pair of L* galaxies at z = 2.92 embedded in a Ly alpha halo of L (Ly alpha ) = (6.2 +/- 1.3) x 10(42) erg s(-1). Globally, the system shows a line profile that is markedly asymmetric and redshifted, but its width and peak shift vary significantly across the halo. By fitting the spatially binned Ly alpha spectra with a collection of radiative transfer galactic wind models, we infer a mean outflow expansion velocity of approximate to 211 km s(-1), with higher values preferentially found on both sides of the system's major axis. The velocity of the outflow is validated with the blueshift of low-ionization metal absorption lines in the spectra of the central galaxies. We also identify a faint (M (1500) approximate to -16.7) companion detected in both Ly alpha and the continuum, whose properties are in agreement with a predicted population of satellite galaxies that contribute to the extended Ly alpha emission. Finally, we briefly discuss the impact of the interaction between the central galaxies on the properties of the halo and the possibility of in situ fluorescent Ly alpha production.

We report spectroscopic confirmations of 15 Ly alpha galaxies at z similar to 7, implying a spectroscopic confirmation rate of similar to 80% on candidates selected from the Ly alpha Galaxies in the Epoch of Reionization (LAGER), which is the largest (24 deg(2)) survey aimed at finding Ly alpha emitters (LAEs) at z similar to 7 and uses deep narrowband imaging from the Dark Energy Camera at CTIO. LAEs at high redshifts are sensitive probes of cosmic reionization, and narrowband imaging is a robust and effective method for selecting a large number of LAEs. In this work, we present results from the spectroscopic follow-up of LAE candidates in two LAGER fields, COSMOS and WIDE-12, using observations from Keck/LRIS. We report the successful detection of Ly alpha emission in 15 candidates. Three of these in COSMOS have matching confirmations from a previous spectroscopic follow-up and are part of the overdense region, LAGER-z7OD1. Two other candidates that were not detected with LRIS have prior spectroscopic confirmations from Magellan. Including these, we obtain a spectroscopic confirmation success rate of similar to 80% for LAGER LAE candidates. Thorough checks were performed to reject the possibility of these detections being foreground emission resulting with a probability of, at most, one contaminant. We do not detect any other UV nebular lines in our LRIS spectra, apart from Ly alpha. We estimate a 2 sigma upper limit for the ratio of N v/Ly alpha, f (NV)/f (Ly alpha ) less than or similar to 0.27. Including confirmations from this work, a total of 33 LAE sources from LAGER are now spectroscopically confirmed. LAGER has more than doubled the sample of spectroscopically confirmed LAE sources at z similar to 7.

We present a new measurement of the Ly alpha luminosity function (LF) at redshift z = 6.9, finding moderate evolution from z = 5.7 that is consistent with a fully or largely ionized z similar to 7 intergalactic medium. Our result is based on four fields of the LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) project. Our survey volume of 6.1 x 10(6) Mpc(3) is double that of the next largest z similar to 7 survey. We combine two new LAGER fields (WIDE12 and GAMA15A) with two previously reported LAGER fields (COSMOS and CDFS). In the new fields, we identify N = 95 new z = 6.9 Ly alpha emitter (LAEs) candidates, characterize our survey's completeness and reliability, and compute Ly alpha LFs. The best-fit Schechter LF parameters for all four LAGER fields are in good general agreement. Two fields (COSMOS and WIDE12) show evidence for a bright-end excess above the Schechter function fit. We find that the Ly alpha luminosity density declines at the same rate as the UV continuum LF from z = 5.7 to 6.9. This is consistent with an intergalactic medium that was fully ionized as early as redshift z similar to 7 or with a volume-averaged neutral hydrogen fraction of x (H I) < 0.33 at 1 sigma.

We introduce a new color selection technique to identify high-redshift, massive galaxies that are systematically missed by Lyman-break selection. The new selection is based on the H-160 (H) and Infrared Array Camera (IRAC) 4.5 mu m bands, specifically H - [4.5] > 2.25 mag. These galaxies, called "HIEROs," include two major populations that can be separated with an additional J - H color. The populations are massive and dusty starforming galaxies at z > 3 (JH - blue) and extremely dusty galaxies at z less than or similar to 3 (JH - red). The 350 arcmin(2) of the GOODS-North and GOODS-South fields with the deepest Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) near-infrared and IRAC data contain as many as 285 HIEROs down to [4.5] < 24 mag. Inclusion of the most extreme HIEROs, not even detected in the H band, makes this selection particularly complete for the identification of massive high-redshift galaxies. We focus here primarily on JH - blue (z > 3) HIEROs, which have a median photometric redshift < z > similar to 4.4 and stellar mass M-* 10(10.6) M-circle dot and are much fainter in the rest-frame UV than similarly massive Lyman-break galaxies (LBGs). Their star formation rates (SFRs), derived from their stacked infrared spectral energy distributions (SEDs), reach similar to 240 M-circle dot yr(-1), leading to a specific SFR, sSFR equivalent to SFR/M-* similar to 4.2 Gyr(-1), suggesting that the sSFRs for massive galaxies continue to grow at z > 2 but at a lower growth rate than from z = 0 to z = 2. With a median half-light radius of 2 kpc, including similar to 20% as compact as quiescent (QS) galaxies at similar redshifts, JH - blue HIEROs represent perfect star-forming progenitors of the most massive (M-* greater than or similar to 10(11.2) M-circle dot) compact QS galaxies at z similar to 3 and have the right number density. HIEROs make up similar to 60% of all galaxies with M-* > 10(10.5) M-circle dot identified at z > 3 from their photometric redshifts. This is five times more than LBGs with nearly no overlap between the two populations. While HIEROs make up 15%-25% of the total SFR density at z similar to 4-5, they completely dominate the SFR density taking place in M-* 10(10.5) M-circle dot galaxies, and HIEROs are therefore crucial to understanding the very early phase of massive galaxy formation.

This work presents the first search for RR Lyrae stars (RRLs) in four he ultrafaint systems imaged by the Dark Energy Survey using SOAR/Goodman and Blanco/DECam imagers, We have detected two RRLs in the field of Grus I, none in Kim 2, one in Phoenix II, and four in Grus II. With the detection of these stars, we accurately determine the distance moduli for these ultrafaint dwarf satellite galaxies; mu(0) = 20.51 +/- 0.10 mag (D-circle dot = 127 +/- 6 kpc) for Grus I and mu(0) = 20.01 +/- 0.10 mag (D-circle dot = 100 +/- 5 kpc) for Phoenix IL These measurements are larger than previous estimations by Koposov et al. and Bechtol et al., implying larger physical sizes; S per cent for Grus I and 33 per cent for Phoenix II. For Grus II, of the four RRLs detected, one is consistent with being a member of the galactic halo (D-circle dot = 24 +/- 1 kpc, mu(0) = 16.86 +/- 0.10 mag), another is at D-circle dot = 55 +/- 2 kpc (mu(0) = 18.71 +/- 0.10 mag), which we associate with Grus II, and the two remaining at D-circle dot = 43 +/- 2 kpc (mu(0) = 18.17 +/- 0.10 mag). Moreover, the appearance of a subtle red horizontal branch in the colour magnitude diagram of Grus II at the same brightness level of the latter two RRLs, which are at the same distance and in the same region, suggests that a more metal-rich system may be located in front of Grus II. The most plausible scenario is the association of these stars with the Chenab/Orphan Stream. Finally, we performed a comprehensive and updated analysis of the number of RRLs in dwarf galaxies. This allows us to predict that the method of finding new ultrafaint dwarf galaxies using two or more clumped RRLs will work only for systems brighter than M-V similar to 6 mag.

We report the results of a systematic search for ultra-faint Milky Way satellite galaxies using data from the Dark Energy Survey (DES) and Pan-STARRS1 (PS1). Together, DES and PS1 provide multi-band photometry in optical/near-infrared wavelengths over similar to 80% of the sky. Our search for satellite galaxies targets similar to 25,000 deg(2) of the high-Galactic-latitude sky reaching a 10 sigma point-source depth of greater than or similar to 22.5 mag in the g and r bands. While satellite galaxy searches have been performed independently on DES and PS1 before, this is the first time that a self-consistent search is performed across both data sets. We do not detect any new high-significance satellite galaxy candidates, recovering the majority of satellites previously detected in surveys of comparable depth. We characterize the sensitivity of our search using a large set of simulated satellites injected into the survey data. We use these simulations to derive both analytic and machine-learning models that accurately predict the detectability of Milky Way satellites as a function of their distance, size, luminosity, and location on the sky. To demonstrate the utility of this observational selection function, we calculate the luminosity function of Milky Way satellite galaxies, assuming that the known population of satellite galaxies is representative of the underlying distribution. We provide access to our observational selection function to facilitate comparisons with cosmological models of galaxy formation and evolution.

We have discovered a large number of circular and elliptical shells at 24 mu m around luminous central sources with MIPS on board the Spitzer Space Telescope. Our archival follow-up effort has revealed 90% of these circumstellar shells to be previously unknown. The majority of the shells is only visible at 24 mu m, but many of the central stars are detected at multiple wavelengths from the mid-to the near-IR regime. The general lack of optical counterparts, however, indicates that these sources represent a population of highly obscured objects. We obtained optical and near-IR spectroscopic observations of the central stars and find most of these objects to be massive stars. In particular, we identify a large population of sources that we argue represents a narrow evolutionary phase, closely related or identical to the luminous blue variable stage of massive stellar evolution.

Nova-like (NL) cataclysmic variables have persistently high mass transfer rates and prominent steady state accretion disks. We present an analysis of infrared observations of 12 NLs obtained from the Two Micron All Sky Survey, the Spitzer Space Telescope, and the Wide-field Infrared Survey Explorer All Sky Survey. The presence of an infrared excess at lambda greater than or similar to 3-5 mu m over the expectation of a theoretical steady state accretion disk is ubiquitous in our sample. The strength of the infrared excess is not correlated with orbital period, but shows a statistically significant correlation (but shallow trend) with system inclination that might be partially (but not completely) linked to the increasing view of the cooler outer accretion disk and disk rim at higher inclinations. We discuss the possible origin of the infrared excess in terms of emission from bremsstrahlung or circumbinary dust, with either mechanism facilitated by the mass outflows (e.g., disk wind/corona, accretion stream overflow, and so on) present in NLs. Our comparison of the relative advantages and disadvantages of either mechanism for explaining the observations suggests that the situation is rather ambiguous, largely circumstantial, and in need of stricter observational constraints.

We present the results of the spectroscopic and photometric monitoring campaign of ASASSN-15ed. The transient was discovered quite young by the All Sky Automated Survey for Super-Novae (ASAS-SN) survey. Amateur astronomers allowed us to sample the photometric SN evolution around maximum light, which we estimate to have occurred on JD=2457087.4 +/- 0.6 in the r band. Its apparent r-band magnitude at maximum was r = 16.91 +/- 0.10, providing an absolute magnitude M-r approximate to -20.04 +/- 0.20, which is slightly more luminous than the typical magnitudes estimated for Type Ibn SNe. The post-peak evolution was well monitored, and the decline rate (being in most bands around 0.1 mag d(-1) during the first 25 d after maximum) is marginally slower than the average decline rates of SNe Ibn during the same time interval. The object was initially classified as a Type Ibn SN because early-time spectra were characterized by a blue continuum with superimposed narrow P-Cygni lines of He I, suggesting the presence of a slowly moving (1200-1500 km s(-1)), He-rich circumstellar medium. Later on, broad P-Cygni He I lines became prominent. The inferred velocities, as measured from the minimum of the broad absorption components, were between 6000 and 7000 km s(-1). As we attribute these broad features to the SN ejecta, this is the first time we have observed the transition of a Type Ibn SN to a Type Ib SN.