69 research outputs found

    The Stellar Mass, Star Formation Rate and Dark Matter Halo Properties of LAEs at z2z\sim2

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    We present average stellar population properties and dark matter halo masses of z2z \sim 2 \lya emitters (LAEs) from SED fitting and clustering analysis, respectively, using \simeq 12501250 objects (NB38725.5NB387\le25.5) in four separate fields of 1\simeq 1 deg2^2 in total. With an average stellar mass of 10.2±1.8×108 M10.2\, \pm\, 1.8\times 10^8\ {\mathrm M_\odot} and star formation rate of 3.4±0.4 M yr13.4\, \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 $4.0_{-2.9}^{+5.1} \times 10^{10}\ {\mathrm M_\odot}withaneffectivebiasof with an effective bias of 1.22^{+0.16}_{-0.18}whichislowerthanthatof which is lower than that of z \sim 2LAEs( LAEs (1.8\, \pm\, 0.3),obtainedbyapreviousstudybasedonathreetimessmallersurveyarea,withaprobabilityof), obtained by a previous study based on a three times smaller survey area, with a probability of 96\%. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low HI gas mass, this result appears to be consistent with the observations of a high \lya escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press-Schechter formalism predicts that at z=0ourLAEsaretypicallyembeddedinhaloswithmassessimilartothatoftheLargeMagellanicCloud(LMC);theywillalsohavesimilarSHMRstotheLMC,iftheirSFRsarelargelysuppressedafter our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their SFRs are largely suppressed after z \sim 2$ as some previous studies have reported for the LMC itself.Comment: 34 pages, 15 figures, 6 tables. Accepted for publication in PAS

    A hard ionizing spectrum in z=3-4 Lyα emitters with intense [OIII] emission: Analogs of galaxies in the reionization era?

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    We present Keck/MOSFIRE spectra of the diagnostic nebular emission lines [O iii]λλ5007,4959, [O ii]λ3727, and Hβ for a sample of 15 redshift z≃3.1\mbox-3.7 Lyα emitters (LAEs) and Lyman break galaxies (LBGs). In conjunction with spectra from other surveys, we confirm earlier indications that LAEs have a much higher [O iii]/[O ii] line ratio than is seen in similar redshift LBGs. By comparing their distributions on a [O iii]/[O ii] versus R23 diagram, we demonstrate that this difference cannot arise solely because of their lower metallicities but most likely is due to a harder ionizing spectrum. Using measures of Hβ and recombination theory, we demonstrate, for a subset of our LAEs, that ξion—the number of Lyman continuum photons per UV luminosity—is indeed 0.2–0.5 dex larger than for typical LBGs at similar redshifts. Using photoionization models, we estimate the effect this would have on both [O iii]/[O ii] and R23 and conclude such a hard spectrum can only partially explain such intense line emission. The additional possibility is that such a large [O iii]/[O ii] ratio is in part due to density rather than ionization bound nebular regions, which would imply a high escape fraction of ionizing photons. We discuss how further observations could confirm this possibility. Clearly LAEs with intense [O iii] emission represent a promising analog of those z > 7 sources with similarly strong lines that are thought to be an important contributor to cosmic reionization

    The dominant origin of diffuse Lyα halos around Lyα emitters explored by spectral energy distribution fitting and clustering analysis

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    The physical origin of diffuse Lyα halos (LAHs) around star-forming galaxies is still a matter of debate. We present the dependence of LAH luminosity [L(Lyα)_H] on the stellar mass (M⋆), star formation rate, color excess [E(B − V)⋆], and dark matter halo mass (M_h) of the parent galaxy for ∼900 Lyα emitters (LAEs) at z ∼ 2 divided into ten subsamples. We calculate L(Lyα)_H using the stacked observational relation between L(Lyα)H and central Lyα luminosity of Momose et al. (2016, MNRAS, 457, 2318), which we find agrees with the average trend of VLT/MUSE-detected individual LAEs. We find that our LAEs have relatively high L(Lyα)_H despite low M⋆ and M_h, and that L(Lyα)_H remains almost unchanged with M⋆ and perhaps with M_h. These results are incompatible with the cold stream (cooling radiation) scenario and the satellite-galaxy star-formation scenario, because the former predicts fainter L(Lyα)_H and both predict steeper L(Lyα)_H vs. M⋆ slopes. We argue that LAHs are mainly caused by Lyα photons escaping from the main body and then scattering in the circum-galactic medium. This argument is supported by LAH observations of Hα emitters (HAEs). When LAHs are taken into account, the Lyα escape fractions of our LAEs are about ten times higher than those of HAEs with similar M⋆ or E(B − V)⋆, which may partly arise from lower H I gas masses implied from lower M_h at fixed M⋆, or from another Lyα source in the central part

    The dominant origin of diffuse Lyα\alpha halos around LAEs explored by SED fitting and clustering analysis

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    The physical origin of diffuse Lyα\alpha halos (LAHs) around star-forming galaxies is still a matter of debate. We present the dependence of LAH luminosity (L(Lyα)HL({\rm Ly}\alpha)_H) on the stellar mass (MM_\star), SFRSFR, color excess (E(BV)E(B-V)_\star), and dark matter halo mass (MhM_{\rm h}) of the parent galaxy for 900\sim 900 Lyα\alpha emitters (LAEs) at z2z\sim2 divided into ten subsamples. We calculate L(Lyα)HL({\rm Ly}\alpha)_H using the stacked observational relation between L(Lyα)HL({\rm Ly}\alpha)_H and central Lyα\alpha luminosity by Momose et al. (2016), which we find agrees with the average trend of VLT/MUSE-detected individual LAEs. We find that our LAEs have relatively high L(Lyα)HL({\rm Ly}\alpha)_H despite low MM_\star and MhM_{\rm h}, and that L(Lyα)HL({\rm Ly}\alpha)_H remains almost unchanged with MM_\star and perhaps with MhM_{\rm h}. These results are incompatible with the cold stream (cooling radiation) scenario and the satellite-galaxy star-formation scenario, because the former predicts fainter L(Lyα)HL({\rm Ly}\alpha)_H and both predict steeper L(Lyα)HL({\rm Ly}\alpha)_H vs. MM_\star slopes. We argue that LAHs are mainly caused by Lyα\alpha photons escaping from the main body and then scattered in the circum-galactic medium. This argument is supported by LAH observations of Hα\alpha emitters (HAEs). When LAHs are taken into account, the Lyα\alpha escape fractions of our LAEs are about ten times higher than those of HAEs with similar MM_\star or E(BV)E(B-V)_\star, which may partly arise from lower HI gas masses implied from lower MhM_{\rm h} at fixed MM_\star, or from another Lyα\alpha source in the central part.Comment: Published in PASJ; 35 pages, 13 figures, 6 table

    Median Surface Brightness Profiles of Lyman-α\alpha Haloes in the MUSE Extremely Deep Field

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    We present the median surface brightness profiles of diffuse Lyα\alpha haloes (LAHs) around star-forming galaxies by stacking 155 spectroscopically confirmed Lyα\alpha emitters (LAEs) at 3<z<4 in the MUSE Extremely Deep Field (MXDF), with median Lyα\alpha luminosity LLyα1041.1ergs1\mathrm{L_{Ly\alpha} \approx 10^{41.1} erg\,s^{-1}}. After correcting for a systematic surface brightness offset we identified in the datacube, we detect extended Lyα\alpha emission out to a distance of 270 kpc. The median Lyα\alpha surface brightness profile shows a power-law decrease in the inner 20 kpc, and a possible flattening trend at larger distance. This shape is similar for LAEs with different Lyα\alpha luminosities, but the normalisation of the surface brightness profile increases with luminosity. At distances larger than 50 kpc, we observe strong overlap of adjacent LAHs, and the Lyα\alpha surface brightness is dominated by the LAHs of nearby LAEs. We find no clear evidence of redshift evolution of the observed Lyα\alpha profiles when comparing with samples at 4<z<5 and 5<z<6. Our results are consistent with a scenario in which the inner 20 kpc of the LAH is powered by star formation in the central galaxy, while the LAH beyond a radius of 50 kpc is dominated by photons from surrounding galaxies.Comment: Submitted to A&
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