16 research outputs found
The impact of nebular emission on the broadband fluxes of high-redshift galaxies
A substantial fraction of the light emitted from young or star-forming
galaxies at ultraviolet to near-infrared wavelengths comes from the ionized
interstellar medium in the form of emission lines and a nebular continuum. At
high redshifts, star formation rates are on average higher and stellar
populations younger than in the local Universe. Both of these effects act to
boost the impact of nebular emission on the overall spectrum of galaxies. Even
so, the broadband fluxes and colours of high-redshift galaxies are routinely
analyzed under the assumption that the light observed originates directly from
stars. Here, we assess the impact of nebular emission on broadband fluxes in
Johnson/Cousins BVRIJHK, Sloan Digital Sky Survey griz and Spitzer IRAC/MIPS
filters as a function of observed redshift (up to z=15) for galaxies with
different star formation histories. We find that nebular emission may account
for a non-negligible fraction of the light received from high-redshift
galaxies. The ages and masses inferred for such objects through the use of
spectral evolutionary models that omit the nebular contribution are therefore
likely to contain systematic errors. We argue that a careful treatment of the
nebular component will be essential for the interpretation of the rest-frame
ultraviolet-to-infrared properties of the first galaxies formed, like the ones
expected to be detected with the James Webb Space Telescope.Comment: 5 pages, 3 figures, accepted for publication in ApJ
Observations of Ly Emitters at High Redshift
In this series of lectures, I review our observational understanding of
high- Ly emitters (LAEs) and relevant scientific topics. Since the
discovery of LAEs in the late 1990s, more than ten (one) thousand(s) of LAEs
have been identified photometrically (spectroscopically) at to . These large samples of LAEs are useful to address two major astrophysical
issues, galaxy formation and cosmic reionization. Statistical studies have
revealed the general picture of LAEs' physical properties: young stellar
populations, remarkable luminosity function evolutions, compact morphologies,
highly ionized inter-stellar media (ISM) with low metal/dust contents, low
masses of dark-matter halos. Typical LAEs represent low-mass high- galaxies,
high- analogs of dwarf galaxies, some of which are thought to be candidates
of population III galaxies. These observational studies have also pinpointed
rare bright Ly sources extended over kpc, dubbed
Ly blobs, whose physical origins are under debate. LAEs are used as
probes of cosmic reionization history through the Ly damping wing
absorption given by the neutral hydrogen of the inter-galactic medium (IGM),
which complement the cosmic microwave background radiation and 21cm
observations. The low-mass and highly-ionized population of LAEs can be major
sources of cosmic reionization. The budget of ionizing photons for cosmic
reionization has been constrained, although there remain large observational
uncertainties in the parameters. Beyond galaxy formation and cosmic
reionization, several new usages of LAEs for science frontiers have been
suggested such as the distribution of {\sc Hi} gas in the circum-galactic
medium and filaments of large-scale structures. On-going programs and future
telescope projects, such as JWST, ELTs, and SKA, will push the horizons of the
science frontiers.Comment: Lecture notes for `Lyman-alpha as an Astrophysical and Cosmological
Tool', Saas-Fee Advanced Course 46. Verhamme, A., North, P., Cantalupo, S., &
Atek, H. (eds.) --- 147 pages, 103 figures. Abstract abridged. Link to the
lecture program including the video recording and ppt files :
https://obswww.unige.ch/Courses/saas-fee-2016/program.cg
Analyzing low signal-to-noise FUSE spectra
Context. Galaxies are believed to be the main providers of Lyman continuum (LyC) photons during the early phases of the cosmic reionization. Little is known however, when it comes to escape fractions and the mechanisms behind the leakage. To learn more, one may look at local objects, but so far only one low-z galaxy has shown any signs of emitting LyC radiation. With data from the Far Ultraviolet Spectroscopic Explorer (FUSE), we previously found an absolute escape fraction of ionizing photons (fesc) of 4–10% for the blue compact galaxy Haro 1
The Lyman continuum escape and ISM properties in Tololo 1247-232-new insights from HST and VLA
Low- and intermediate-mass galaxies are widely discussed as cause of reionization at redshift z similar to 10-6. However, observational proof of galaxies that are leaking ionizing radiation (Lyman continuum; LyC) is a currently ongoing challenge and the list of LyC emitting candidates is still short. Tololo 1247-232 is among those very few galaxies with recently reported leakage. We performed intermediate resolution ultraviolet spectroscopy with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope and confirm ionizing radiation emerging from Tololo 1247-232. Adopting an improved data reduction procedure, we find that LyC escapes from the central stellar clusters, with an escape fraction of 1.5 +/- 0.5 per cent only, i.e. the lowest value reported for the galaxy so far. We further make use of far-ultraviolet absorption lines of Si II and Si IV as a probe of the neutral and ionized interstellar medium ( ISM). We find that most of the ISM gas is ionized, likely facilitating LyC escape from density bounded regions. Neutral gas covering as a function of line-of-sight velocity is derived using the apparent optical depth method. The ISM is found to be sufficiently clumpy, supporting the direct escape of LyC photons. We further report on broad-band UV and optical continuum imaging as well as narrow-band imaging of Lya, Ha and H beta. Using stellar population synthesis, an Lya escape fraction of 8 per cent was derived. We also performed Very Large Array 21cm imaging. The hydrogen hyperfine transition was not detected, but a deep upper limit atomic gas mass of less than or similar to 10(9) M-circle dot could be derived. The upper limit gas fraction defined as M-HI/M-* is only 20 per cent. Evidence is found that the HI gas halo is relatively small compared to the Lyman Alpha Reference Sample (Hayes et al. 2013, 2014; Ostlin et al. 2014)