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Register a new userInteracting LAEs at z = 5.1. Episodic star formation in a group of LAEs at z= 5.07
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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).
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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 present average stellar population properties and dark matter halo masses of $z sim 2$ lya emitters (LAEs) from SED fitting and clustering analysis, respectively, using $simeq$ $1250$ objects ($NB387le25.5$) in four separate fields of $simeq 1$ deg$^2$ in total. With an average stellar mass of $10.2, pm, 1.8times 10^8 {mathrm M_odot}$ and star formation rate of $3.4, pm, 0.4 {mathrm M_odot} {rm yr^{-1}}$, the LAEs lie on an extrapolation of the star-formation main sequence (MS) to low stellar mass. Their effective dark matter halo mass is estimated to be $4.0_{-2.9}^{+5.1} times 10^{10} {mathrm M_odot}$ with an effective bias of $1.22^{+0.16}_{-0.18}$ which is lower than that of $z sim 2$ LAEs ($1.8, pm, 0.3$), obtained by a previous study based on a three times smaller survey area, with a probability of $96%$. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low HI gas mass, this result appears to be consistent with the observations of a high lya escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press-Schechter formalism predicts that at $z=0$ our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their SFRs are largely suppressed after $z sim 2$ as some previous studies have reported for the LMC itself.
We searched massive galaxy population in the known large-scale high-density structure of Lyman$~alpha$ emitters (LAEs) at $z=2.39$ near the radio galaxy 53W002 by using $B,~V,~i^prime,~J,~H,$ and $~K_s$-bands imaging data taken with Suprime-Cam and MOIRCS on the Subaru telescope. We selected 62 protocluster member candidates by their $JHK_s$-band colors and photometric redshift analysis ($JHK_s$-selected galaxies) in our survey field of $70.2~{rm{arcmin}}^{2}$, and compared their physical properties estimated from the SED fitting with a comparison sample in the COSMOS field. We found significant number density excesses for the $JHK_s$-selected galaxies in the 53W002 field at $K_s<22.25,~J-K_s>2,$ or $V-K_s>4$. In particular the number density of the $JHK_s$-selected galaxies with $K_s<22.25$ and $J-K_s>2$ in the 53W002 field is eight times higher than the comparison sample. Most of those with $K_s<22.25$ and $J-K_s>2$ are massive galaxies with $M_s>10^{11}~M_odot$, and their sSFRs of $10^{-11}$--$10^{-10}~rm{yr^{-1}}$ suggest that the star formation has not yet stopped completely. We also found a density excess of quiescent galaxies with $M_s=5times10^{10}$--$10^{11}~M_odot$ and ${rm{sSFR}}<10^{-11}~rm{yr^{-1}}$ as well as that of low-mass galaxies with $M_s=10^{9.75}$--$10^{10}~M_odot$ and various sSFRs. The massive galaxies with $M_s>10^{11}~M_odot$ are not located at the density peaks of LAEs, but they show a wide distribution along the similar direction with the structure of LAEs over $sim15$--$20$ comoving Mpc. On the other hand, the quiescent galaxies with ${rm{sSFR}}<10^{-11}~rm{yr^{-1}}$ clearly avoid the structure of LAEs. Our results suggest that massive galaxies also exist in this protocluster discovered by the moderate overdensity of LAEs and their star formation activity depends on location in the protocluster.
Aims. We present a spectroscopic study of the properties of 64 Balmer break galaxies that show signs of star formation. The studied sample of star-forming galaxies spans a redshift range from 0.094 to 1.475 with stellar masses in the range 10$^{8}-$10$^{12}$ $M_{odot}$. The sample also includes eight broad emission line galaxies with redshifts between 1.5 $<z<$ 3.0. Methods. We derived star formation rates (SFRs) from emission line luminosities and investigated the dependence of the SFR and specific SFR (SSFR) on the stellar mass and color. Furthermore, we investigated the evolution of these relations with the redshift. Results. We found that the SFR correlates with the stellar mass, our data is consistent with previous results from other authors in that there is a break in the correlation, which reveals the presence of massive galaxies with lower SFR values (i.e., decreasing star formation). We also note an anticorrelation for the SSFR with the stellar mass. Again in this case, our data is also consistent with a break in the correlation, revealing the presence of massive star-forming galaxies with lower SSFR values, thereby increasing the anticorrelation. These results might suggest a characteristic mass ($M_{0}$) at which the red sequence could mostly be assembled. In addition, at a given stellar mass, high-redshift galaxies have on average higher SFR and SSFR values than local galaxies. Finally, we explored whether a similar trend could be observed with redshift in the SSFR$-(u-B)$ color diagram, and we hypothesize that a possible $(u-B)_{0}$ break color may define a characteristic color for the formation of the red sequence.
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