Ly-alpha emission in low-redshift most metal-deficient compact star-forming galaxies
Y. I. Izotov, T. X. Thuan, N. G. Guseva, D. Schaerer, G. Worseck, A. Verhamme
备注:
19 pages, 9 figures, acccepted for publication in Monthly Notices of the Royal Astronomical Society. arXiv admin note: text overlap with arXiv:1910.12773
We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of nine most metal-deficient compact star-forming galaxies with oxygen abundances 12+log(O/H)=6.97-7.23, redshifts z=0.02811-0.13320, and stellar masses M*<10^7Msun. We aim to study the properties of Ly-alpha emission in these extremely metal-deficient objects. We find that all nine galaxies are Ly-alpha emitters (LAEs). We examine various relations between the Ly-alpha escape fraction fesc(Ly-alpha) and other characteristics - such as absolute UV magnitude, oxygen abundance, O32 ratio, stellar mass, Lyman-alpha luminosity and equivalent width EW(Ly-alpha), ionizing photon production efficiency and velocity separation Vsep between the two peaks of the Ly-alpha profile - of a large sample of LAEs, including our lowest-metallicity galaxies and other objects from the literature. We find a relatively tight correlation between fesc(Ly-alpha) and two characteristics, EW(Ly-alpha) and Vsep, whereas no correlation is found between fesc(Ly-alpha) and the oxygen abundance. We also find a relatively tight relation between the Ly-alpha and LyC escape fractions. We propose to use the latter relation to estimate indirectly the escaping ionizing radiation in LAEs, when direct measurements of LyC emission are not possible. We show that the global properties of low-z LAEs are very similar to those of z>6 galaxies. They are thus ideal local proxies for studying physical processes during the epoch of reionization of the Universe.
Recently, Kojima and co-authors have reported a record low oxygen abundance, 12+logO/H=6.90+/-0.03 in the low-mass star-forming galaxy HSC J1631+4426. This exceptionally low oxygen abundance was obtained by the direct method, using the [OIII]4363 emission line. However, using the strong-line method by Izotov et al. (2019b), these authors have derived a significantly higher metallicity 12+logO/H=7.175+/-0.005. To clarify the situation, we have obtained new observations of HSC J1631+4426 with the Large Binocular Telescope (LBT)/Multi-Object Dual Spectrograph (MODS). We have derived a higher oxyg…
We perform a deep wide-field imaging survey of nearby galaxies using H$α$ and broadband filters to investigate the characteristics of star formation in galaxies. Motivated by the finding that star formation rates (SFRs) derived from H$α$ fluxes in dwarf galaxies are systematically lower than those inferred from far-ultraviolet (FUV) fluxes, we attempt to determine whether the same trend exists in the extended disks of two star-forming galaxies. We perform spatially resolved photometry using grid-shaped apertures to measure the FUV and H$α$ fluxes of star-forming regions. We also perform spectr…
Integral field unit (IFU) spectra of face-on star-forming galaxies from the MaNGA survey are stacked in radial bins so as to reach a S/N high enough to measure emission lines and Lick indices out to 2.5-3 R_e. Two thirds of galaxies have stellar populations in the outer disks that are older, more metal poor and less dusty than in the inner disks. Recent bursts of star formation have occurred more frequently in the outer disk, but extinction-corrected Halpha equivalent widths are significantly lower at fixed D_n(4000) in these regions. I examine the properties of a subset of galaxies with the t…
We report on the discovery of extended Ly-alpha nebulae at z~3.3 in the Hubble Ultra Deep Field (HUDF, ~ 40 kpc X 80 kpc) and behind the Hubble Frontier Fields galaxy cluster MACSJ0416 (~ 40kpc), spatially associated with groups of star-forming galaxies. VLT/MUSE integral field spectroscopy reveals a complex structure with a spatially-varying double peaked Ly-alpha emission. Overall, the spectral profiles of the two Ly-alpha nebulae are remarkably similar, both showing a prominent blue emission, more intense and slightly broader than the red peak. From the first nebula, located in the HUDF, no…
We use Hubble space telescope data of 45 nearby star-forming galaxies to investigate properties of Lyman-alpha (Ly$α$) halos, Ly$α$ morphology, and the star-forming characteristics of galaxies. We study how the morphology of Ly$α$ emission is related to other Ly$α$ observables. Furthermore, we study the interdependencies of Ly$α$ morphological quantities. We studied the spatial extent of Ly$α$ using surface brightness profiles in i) using circular apertures and ii) within faint Ly$α$ isophotes. We measured the average intensity and the size of the regions with a high star formation rate densit…
We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of seven compact low-mass star-forming galaxies at redshifts, z,in the range 0.3161-0.4276, with various O3Mg2=[OIII]5007/MgII 2796+2803 and Mg2=MgII 2796/MgII 2803 emission-line ratios. We aim to study the dependence of leaking Lyman continuum (LyC) emission on the characteristics of MgII emission together with the dependences on other indirect indicators of escaping ionizing radiation. LyC emission with escape fractions fesc(LyC)=3.1-4.6 per cent is detected in four galaxies, whereas only 1sigma u…
We perform Lyman-alpha radiative transfer calculations for reproducing Lyman-alpha properties of star-forming galaxies at high redshifts. We model a galaxy as a halo in which the density distributions of Lyman-alpha sources and H I plus dust medium are described with exponential functions. We also consider an outflow of the medium that represents a momentum-driven wind in a gravitational potential well. We successfully reproduce both the spectra and the surface brightness profiles of eight star-forming galaxies at z =3-6 observed with MUSE using this outflowing halo model with Lyman-alpha scat…
We present ~0.15'' spatial resolution imaging of SHiZELS-14, a massive (M*~10^11 M_sol), dusty, star-forming galaxy at z=2.24. Our rest-frame ~1kpc-scale, matched-resolution data comprise four different widely used tracers of star formation: the H-alpha emission line (from SINFONI/VLT), rest-frame UV continuum (from HST F606W imaging), the rest-frame far-infrared (from ALMA), and the radio continuum (from JVLA). Although originally identified by its modest H-alpha emission line flux, SHiZELS-14 appears to be a vigorously star-forming (SFR~1000 M_sol/yr) example of a submillimeter galaxy, proba…
The Lyman-alpha and Continuum Origins Survey II: the connection between the escape of ionizing radiation and Lyman-alpha halos in star-forming galaxies
Stockholm University(斯德哥尔摩大学);University of Minnesota(明尼苏达大学);Johns Hopkins University(约翰斯·霍普金斯大学);Space Telescope Science Institute(太空望远镜科学研究所);CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, Univ Lyon, Ens de Lyon(法国国家科学研究中心,里昂天体物理研究中心UMR5574,里昂大学,里昂高等师范学校);Observatoire de Genève, Université de Genève(日内瓦天文台,日内瓦大学)
Extended Lyman-alpha emission is now commonly detected around high redshift galaxies through stacking and even on individual basis. Despite recent observational advances, the physical origin of these Lyman-alpha halos (LAHs), as well as their relationships to galaxies, quasars, circumgalactic gas, and other environmental factors remains unclear. We present results from our new Lyman-alpha full radiative transfer code voroILTIS which runs directly on the unstructured Voronoi tessellation of cosmological hydrodynamical simulations. We make use of the TNG50 simulation and simulate LAHs from redsh…
Star-forming rings in lenticular galaxies: origin of the gas
S 0中的环是神秘的特征,然而它可以泄露特定星系的演化路径。我们已经进行了长缝光谱的五个透镜状星系的紫外线明亮的外环。这些观测是用南部非洲大望远镜(SALT)进行的,目的是揭示恒星星族的运动学、化学和年龄,以及环和周围圆盘中的气体特征。五个环中有四个在H-α发射线上也很明亮,在H-α等效宽度最大值附近提取的气体环光谱显示出年轻恒星的激发,这表明环中目前正在形成恒星。这个恒星形成的整体水平是每年0.1-0.2个太阳质量,在NGC 7808中的突出值是每年1个太阳质量。环中电离气体的化学成分与金属丰度接近太阳的恒星盘之间的差异意味着最近的气体吸积和恒星形成点火;通过使用不同的恒星形成指标估计的恒星形成历史意味着恒星形成率随着e折叠时间的减少而减少。在NGC 809中,紫外环清晰可见,但没有大质量恒星激发的H-α发射线,恒星形成已经停止。
ReveaLLAGN 1: JWST Emission-Line Spectra Reveal Low-Luminosity AGN with UV-Deficient SEDs and Warm Molecular Gas
University of Utah(犹他大学);Vanderbilt University(范德堡大学);Centro de Estudios de Física del Cosmos de Aragón (CEFCA)(阿拉贡宇宙物理研究中心);European Space Agency(欧洲空间局);Max-Planck-Institut für Astronomie(马克斯·普朗克天文学研究所);The Pennsylvania State University(宾夕法尼亚州立大学);Istituto di Astrofisica e Planetologia Spaziali (INAF–IAPS)(国家天体物理学和行星学研究所)
We discovered an over-density of H-alpha-emitting galaxies associated with a Planck compact source in the COSMOS field (PHzG237.0+42.5) through narrow-band imaging observations with Subaru/MOIRCS. This Planck-selected dusty proto-cluster at z=2.16 has 38 H-alpha emitters including six spectroscopically confirmed galaxies in the observed MOIRCS 4'x7' field (corresponding to ~2.0x3.5~Mpc^2 in physical scale). We find that massive H-alpha emitters with log(M*/Msun)>10.5 are strongly clustered in the core of the proto-cluster (within ~300-kpc from the density peak of the H-alpha emitters). Most of…