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Register a new userRadio continuum emission from local analogs of high-z faint LAEs: Blueberry galaxies
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We present a radio continuum study of a population of extremely young and starburst galaxies, termed as blueberries at ${sim}$ 1 GHz using the upgraded Giant Metrewave Radio Telescope (uGMRT). We find that their radio-based star formation rate (SFR) is suppressed by a factor of ${sim}$ 3.4 compared to the SFR based on optical emission lines. This might be due to (i) the young ages of these galaxies as a result of which a stable equilibrium via feedback from supernovae has not yet been established (ii) escape of cosmic ray electrons via diffusion or galactic scale outflows. The estimated non-thermal fraction in these galaxies has a median value of ${sim}$0.49, which is relatively lower than that in normal star-forming galaxies at such low frequencies. Their inferred equipartition magnetic field has a median value of 27 ${mu}$G, which is higher than those in more evolved systems like spiral galaxies. Such high magnetic fields suggest that small-scale dynamo rather than large-scale dynamo mechanisms might be playing a major role in amplifying magnetic fields in these galaxies.
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We are undertaking a search for high-redshift low luminosity Lyman Alpha sources in the SHARDS survey. Among the pre-selected Lyman Alpha sources 2 candidates were spotted, located 3.19 arcsec apart, and tentatively at the same redshift. Here we report on the spectroscopic confirmation with GTC of the Lyman Alpha emission from this pair of galaxies at a confirmed spectroscopic redshifts of z=5.07. Furthermore, one of the sources is interacting/merging with another close companion that looks distorted. Based on the analysis of the spectroscopy and additional photometric data, we infer that most of the stellar mass of these objects was assembled in a burst of star formation 100 Myr ago. A more recent burst (2 Myr old) is necessary to account for the measured Lyman Alpha flux. We claim that these two galaxies are good examples of Lyman Alpha sources undergoing episodic star formation. Besides, these sources very likely constitute a group of interacting Lyman Alpha emitters (LAEs).
Star-forming dwarf galaxies have properties similar to those expected in high-redshift galaxies. Hence, these local galaxies may provide insights into the evolution of the first galaxies, and the physical processes at work. We present a sample of eleven potential local analogs to high-$z$ (LAHz) galaxies. The sample consists of blue compact dwarf galaxies, selected to have spectral energy distributions that fit galaxies at $1.5<z<4$. We use SOFIA-HAWC+ observations combined with optical and near-infrared data to characterize the dust properties, star formation rate (SFR) and star formation histories (SFH) of the sample of LAHz. We employ Bayesian analysis to characterize the dust using two-component black-body models. Using the LIGHTNING package we fit the spectral energy distribution of the LAHz galaxies over the FUV-FIR wavelength range, and derive the SFH in five time-steps up to a look-back time of 13.3 Gyr. Of the eleven LAHz candidates, six galaxies have SFH consistent with no star formation activity at look-back times beyond 1 Gyr. The remaining galaxies show residual levels of star formation at ages $gtrsim$1,Gyr, making them less suitable as local analogs. The six young galaxies stand out in our sample by having the lowest gas-phase metallicities. They are characterized by warmer dust, having the highest specific SFR, and the highest gas mass fractions. The young age of these six galaxies suggests that merging is less important as a driver of the star formation activity. The six LAHz candidates are promising candidates for studies of the gas dynamics role in driving star formation.
We study the average Ly$alpha$ emission associated with high-$z$ strong (log $N$(H I) $ge$ 21) damped Ly$alpha$ systems (DLAs). We report Ly$alpha$ luminosities ($L_{rm Lyalpha}$) for the full as well as various sub-samples based on $N$(H I), $z$, $(r-i)$ colours of QSOs and rest equivalent width of Si II$lambda$1526 line (i.e., $W_{1526}$). For the full sample, we find $L_{rm Lyalpha}$$< 10^{41} (3sigma) rm erg s^{-1}$ with a $2.8sigma$ level detection of Ly$alpha$ emission in the red part of the DLA trough. The $L_{rm Lyalpha}$ is found to be higher for systems with higher $W_{1526}$ with its peak, detected at $geq 3sigma$, redshifted by about 300-400 $rm km s^{-1}$ with respect to the systemic absorption redshift, as seen in Lyman Break Galaxies (LBGs) and Ly$alpha$ emitters. A clear signature of a double-hump Ly$alpha$ profile is seen when we consider $W_{1526} ge 0.4$ AA and $(r-i) < 0.05$. Based on the known correlation between metallicity and $W_{1526}$, we interpret our results in terms of star formation rate (SFR) being higher in high metallicity (mass) galaxies with high velocity fields that facilitates easy Ly$alpha$ escape. The measured Ly$alpha$ surface brightness requires local ionizing radiation that is 4 to 10 times stronger than the metagalactic UV background at these redshifts. The relationship between the SFR and surface mass density of atomic gas seen in DLAs is similar to that of local dwarf and metal poor galaxies. We show that the low luminosity galaxies will contribute appreciably to the stacked spectrum if the size-luminosity relation seen for H I at low-$z$ is also present at high-$z$. Alternatively, large Ly$alpha$ halos seen around LBGs could also explain our measurements.
We conduct a 350 micron dust continuum emission survey of 17 dust-obscured galaxies (DOGs) at z = 0.05-0.08 with the Caltech Submillimeter Observatory (CSO). We detect 14 DOGs with S_350 = 114-650 mJy and S/N > 3. By including two additional DOGs with submillimeter data in the literature, we are able to study dust contents for a sample of 16 local DOGs that consists of 12 bump and 4 power-law types. We determine their physical parameters with a two-component modified blackbody function model. The derived dust temperatures are in the range 57-122 K and 22-35 K for the warm and cold dust components, respectively. The total dust mass and the mass fraction of warm dust component are 3-34$times10^{7} M_odot$ and 0.03-2.52%, respectively. We compare these results with those of other submillimeter-detected infrared luminous galaxies. The bump DOGs, the majority of the DOG sample, show similar distributions of dust temperatures and total dust mass to the comparison sample. The power-law DOGs show a hint of smaller dust masses than other samples, but need to be tested with a larger sample. These findings support that the reason why DOGs show heavy dust obscuration is not an overall amount of dust content, but probably the spatial distribution of dust therein.
We present a deep Hubble Space Telescope (HST) imaging study of two dwarf galaxies in the halos of Local Volume Large Magellanic Cloud (LMC) analogs. These dwarfs were discovered as part of our Subaru+Hyper Suprime-Cam MADCASH survey: MADCASH-1, which is a satellite of NGC 2403 (D~3.2 Mpc), and MADCASH-2, a previously unknown dwarf galaxy near NGC 4214 (D~3.0 Mpc). Our HST data reach >3.5 mag below the tip of the red giant branch (TRGB) of each dwarf, allowing us to derive their structural parameters and assess their stellar populations. We measure TRGB distances ($D=3.41^{+0.24}_{-0.23}$ Mpc for MADCASH-1, and $D=3.00^{+0.13}_{-0.15}$ Mpc for MADCASH-2), and confirm their associations with their host galaxies. MADCASH-1 is a predominantly old, metal-poor stellar system (age ~13.5 Gyr, [M/H] ~ -2.0), similar to many Local Group dwarfs. Modelling of MADCASH-2s CMD suggests that it contains mostly ancient, metal-poor stars (age ~13.5 Gyr, [M/H] ~ -2.0), but that ~10% of its stellar mass was formed 1.1--1.5 Gyr ago, and ~1% was formed 400--500 Myr ago. Given its recent star formation, we search MADCASH-2 for neutral hydrogen using the Green Bank Telescope, but find no emission and estimate an upper limit on the HI mass of $<4.8times10^4 M_{odot}$. These are the faintest dwarf satellites known around host galaxies of LMC mass outside the Local Group ($M_{V,text{MADCASH-1}}=-7.81pm0.18$, $M_{V,text{MADCASH-2}}=-9.15pm0.12$), and one of them shows signs of recent environmental quenching by its host. Once the MADCASH survey for faint dwarf satellites is complete, our census will enable us to test CDM predictions for hierarchical structure formation, and discover the physical mechanisms by which low-mass hosts influence the evolution of their satellites.
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