Abstract
Compact starburst galaxies are thought to include many or most of the galaxies from which substantial Lyman continuum emission can escape into the intergalactic medium. Li & Malkan used ...Sloan Digital Sky Survey photometry to find a population of such starburst galaxies at
z
∼ 0.5. They were discovered by their extremely strong O
iii
λλ
4959+5007 emission lines, which produce a clearly detectable excess brightness in the
i
bandpass, compared with surrounding filters. We therefore used the Hubble Space Telescope (HST)/COS spectrograph to observe two of the newly discovered
i
-band excess galaxies around their Lyman limits. One has strongly detected continuum below its Lyman limit, corresponding to a relative escape fraction of ionizing photons of 20% ± 2%. The other, which is less compact in UV imaging, has a 2
σ
upper limit to its Lyman escape fraction of <5%. Before the UV spectroscopy, the existing data could not distinguish these two galaxies. Although a sample of two is hardly sufficient for statistical analysis, it shows the possibility that some fraction of these strong O
iii
emitters as a class have ionizing photons escaping. The differences might be determined by the luck of our particular viewing geometry. Obtaining the HST spectroscopy revealed that the Lyman-continuum-emitting galaxy differs in having no central absorption in its prominent Ly
α
emission-line profile. The other target, with no escaping Lyman continuum, shows the more common double-peaked Ly
α
emission.
Abstract
Detections and non-detections of Lyman alpha (Lyα) emission from z > 6 galaxies (<1 Gyr after the big bang) can be used to measure the timeline of cosmic reionization. Of key interest to ...measuring reionization’s mid-stages, but also increasing observational challenge, are observations at z > 7, where Lyα redshifts to near infra-red wavelengths. Here we present a search for z > 7.2 Lyα emission in 53 intrinsically faint Lyman Break Galaxy candidates, gravitationally lensed by massive galaxy clusters, in the KMOS Lens-Amplified Spectroscopic Survey (KLASS). With integration times of ∼7–10 h, we detect no Lyα emission with signal-to-noise ratio (S/N) > 5 in our sample. We determine our observations to be 80 per cent complete for 5σ spatially and spectrally unresolved emission lines with integrated line flux >5.7 × 10−18 erg s−1 cm−2. We define a photometrically selected sub-sample of 29 targets at z = 7.9 ± 0.6, with a median 5σ Lyα EW limit of 58 Å. We perform a Bayesian inference of the average intergalactic medium (IGM) neutral hydrogen fraction using their spectra. Our inference accounts for the wavelength sensitivity and incomplete redshift coverage of our observations, and the photometric redshift probability distribution of each target. These observations, combined with samples from the literature, enable us to place a lower limit on the average IGM neutral hydrogen fraction of $\gt 0.76 \,\, (68{{\ \rm per\ cent}}), \,\, \gt 0.46 \,\, (95{{\ \rm per\ cent}})$ at z ∼ 8, providing further evidence of rapid reionization at z ∼ 6–8. We show that this is consistent with reionization history models extending the galaxy luminosity function to $M_ \rm {\small UV}\lesssim -12$, with low ionizing photon escape fractions, $f_\textrm{esc} \lesssim 15{{\ \rm per\ cent}}$.
ABSTRACT We have previously calculated the intergalactic background light (IBL) as a function of redshift from the Lyman limit in the far-ultraviolet to a wavelength of 5 m in the near-infrared ...range, based purely on data from deep galaxy surveys. Here, we use similar methods to determine the mid- and far-infrared IBL from 5 to 850 m. Our approach enables us to constrain the range of photon densities by determining the uncertainties in observationally determined luminosity densities and spectral gradients. By also including the effect of the 2.7 K cosmic background photons, we determine upper and lower limits on the opacity of the universe to γ-rays up to PeV energies within a 68% confidence band. Our direct results on the IBL are consistent with those from complimentary γ-ray analyses using observations from the Fermi γ-ray space telescope and the H.E.S.S. air erenkov telescope. Thus, we find no evidence of previously suggested processes for the modification of γ-ray spectra other than that of absorption by pair production alone.
Recent radio surveys have discovered a large number of low-luminosity core-dominated radio galaxies that are much more abundant than those at higher luminosities. These objects will be too faint in ...γ-rays to be detected individually by Fermi. Nevertheless, they may contribute significantly to the unresolved extragalactic γ-ray background. We consider here the possible contribution of these core-dominated radio galaxies to the diffuse extragalactic γ-ray background. Using published data available for all 45 of the radio galaxies listed as detected counterparts in the Fermi FL8Y source list update to the 3FGL catalog, we have searched for radio maps that can resolve the core flux from the total source flux. Using high-resolution radio maps we were able to obtain core fluxes for virtually every source. We then derived a relation between core radio flux and γ-ray flux that we extrapolated to sources with low radio luminosities that are known to be highly core-dominated. We then employed a very recent determination of the luminosity function for core-dominated radio galaxies in order to obtain the contribution of all possible γ-ray-emitting radio galaxies to the unresolved extragalactic γ-ray background. We find this contribution to be possibly non-negligible, 4%-18% of the unresolved γ-ray background observed using the Fermi-LAT telescope.
The observed scatter in intergalactic Ly opacity at z 6 requires large-scale fluctuations in the neutral fraction of the intergalactic medium (IGM) after the expected end of reionization. ...Post-reionization models that explain this scatter invoke fluctuations in either the ionizing ultraviolet background (UVB) or IGM temperature. These models make very different predictions, however, for the relationship between Ly opacity and local density. Here, we test these models using Ly -emitting galaxies (LAEs) to trace the density field surrounding the longest and most opaque known Ly trough at z < 6. Using deep Subaru Hyper Suprime-Cam narrowband imaging, we find a highly significant deficit of z 5.7 LAEs within 20 of the trough. The results are consistent with a model in which the scatter in Ly opacity near z ∼ 6 is driven by large-scale UVB fluctuations, and disfavor a scenario in which the scatter is primarily driven by variations in IGM temperature. UVB fluctuations at this epoch present a boundary condition for reionization models, and may help shed light on the nature of the ionizing sources.
ABSTRACT We present the first results from MMT and Keck spectroscopy for a large sample of emission-line galaxies selected from our narrowband imaging in the Subaru Deep Field. We measured the weak O ...iii λ4363 emission line for 164 galaxies (66 with at least 3 detections, and 98 with significant upper limits). The strength of this line is set by the electron temperature for the ionized gas. Because the gas temperature is regulated by the metal content, the gas-phase oxygen abundance is inversely correlated with O iii λ4363 line strength. Our temperature-based metallicity study is the first to span Gyr of cosmic time and dex in stellar mass for low-mass galaxies, -9.0. Using extensive multi-wavelength photometry, we measure the evolution of the stellar mass-gas metallicity relation and its dependence on dust-corrected star formation rate (SFR). The latter is obtained from high signal-to-noise Balmer emission-line measurements. Our mass-metallicity relation is consistent with Andrews & Martini at , and evolves toward lower abundances at a given stellar mass, . We find that galaxies with lower metallicities have higher SFRs at a given stellar mass and redshift, although the scatter is large ( dex) and the trend is weaker than seen in local studies. We also compare our mass-metallicity relation against predictions from high-resolution galaxy formation simulations, and find good agreement with models that adopt energy- and momentum-driven stellar feedback. We identified 16 extremely metal-poor galaxies with abundances of less than a tenth of solar; our most metal-poor galaxy at is similar to I Zw 18.
Abstract
We measure the bolometric luminosity of a complete and unbiased 12
μ
m-selected sample of active galactic nuclei (AGN) in the local Universe. For each galaxy, we used a 10-band ...radio-to-X-ray spectral energy distribution (SED) to isolate the genuine AGN continuum in each band, including subarcsecond measurements where available, and correcting those contaminated by the host galaxy. We derive the median SED of Seyfert type 1 AGN, Seyferts with hidden broad lines (HBLs), Seyferts of type 2, and LINER nuclei in our sample. The median Seyfert 1 SED shows the characteristic blue bump feature in the UV, but nevertheless, the largest contribution to the bolometric luminosity comes from the IR and X-ray continua. The median SEDs of both HBL and type 2 AGN are affected by starlight contamination in the optical/UV. The median SED of HBL AGN is consistent with that of Seyfert 1s, when an extinction of
A
V
∼ 1.2 mag is applied. The comprehensive SEDs allowed us to measure accurate bolometric luminosities and derive robust bolometric corrections for the different tracers. The 12
μ
m and
K
-band nuclear luminosities have good linear correlations with the bolometric luminosity, similar to those in the X-rays. We derive bolometric corrections for either continuum bands (
K
band, 12
μ
m, 2–10 keV, and 14–195 keV) or narrow emission lines (mid-IR high-ionization lines of O
iv
and Ne
v
and optical O
iii
5007 Å) as well as for combinations of IR continuum and line emission. A combination of continuum plus line emission accurately predicts the bolometric luminosity up to quasar luminosities (∼10
46
erg s
−1
).
ABSTRACT We present a coherent database of spectroscopic observations of far-IR fine-structure lines from the Herschel/Photoconductor Array Camera and Spectrometer archive for a sample of 170 local ...active galactic nuclei (AGNs), plus a comparison sample of 20 starburst galaxies and 43 dwarf galaxies. Published Spitzer/IRS and Herschel/SPIRE line fluxes are included to extend our database to the full 10-600 m spectral range. The observations are compared to a set of Cloudy photoionization models to estimate the above physical quantities through different diagnostic diagrams. We confirm the presence of a stratification of gas density in the emission regions of the galaxies, which increases with the ionization potential of the emission lines. The new O iv /O iii versus Ne iii /Ne ii diagram is proposed as the best diagnostic to separate (1) AGN activity from any kind of star formation and (2) low-metallicity dwarf galaxies from starburst galaxies. Current stellar atmosphere models fail to reproduce the observed O iv /O iii ratios, which are much higher when compared to the predicted values. Finally, the (Ne iii + Ne ii )/(S iv +S iii ) ratio is proposed as a promising metallicity tracer to be used in obscured objects, where optical lines fail to accurately measure the metallicity. The diagnostic power of mid- to far-infrared spectroscopy shown here for local galaxies will be of crucial importance to study galaxy evolution during the dust-obscured phase at the peak of the star formation and black hole accretion activity ( ). This study will be addressed by future deep spectroscopic surveys with present and forthcoming facilities such as the James Webb Space Telescope, the Atacama Large Millimeter/submillimeter Array, and the Space Infrared telescope for Cosmology and Astrophysics.
ABSTRACT We present the discovery of three protoclusters at z ∼ 3-4 with spectroscopic confirmation in the Canada-France-Hawaii Telescope Legacy Survey Deep Fields. In these fields, we investigate ...the large-scale projected sky distribution of z ∼ 3-6 Lyman-break galaxies and identify 21 protocluster candidates from regions that are overdense at more than 4 overdensity significance. Based on cosmological simulations, it is expected that more than 76% of these candidates will evolve into a galaxy cluster of at least a halo mass of 1014 M at z = 0. We perform follow-up spectroscopy for eight of the candidates using Subaru/FOCAS, Keck II/DEIMOS, and Gemini-N/GMOS. In total we target 462 dropout candidates and obtain 138 spectroscopic redshifts. We confirm three real protoclusters at z = 3-4 with more than five members spectroscopically identified and find one to be an incidental overdense region by mere chance alignment. The other four candidate regions at z ∼ 5-6 require more spectroscopic follow-up in order to be conclusive. A z = 3.67 protocluster, which has 11 spectroscopically confirmed members, shows a remarkable core-like structure composed of a central small region (<0.5 physical Mpc) and an outskirts region (∼1.0 physical Mpc). The Ly equivalent widths of members of the protocluster are significantly smaller than those of field galaxies at the same redshift, while there is no difference in the UV luminosity distributions. These results imply that some environmental effects start operating as early as at z ∼ 4 along with the growth of the protocluster structure. This study provides an important benchmark for our analysis of protoclusters in the upcoming Subaru/HSC imaging survey and its spectroscopic follow-up with the Subaru/PFS that will detect thousands of protoclusters up to z ∼ 6.
Abstract
The MAMMOTH–Grism slitless spectroscopic survey is a Hubble Space Telescope (HST) cycle 28 medium program, which is obtaining 45 orbits of WFC3/IR grism spectroscopy in the density peak ...regions of three massive galaxy protoclusters at
z
= 2–3 discovered using the MAMMOTH technique. We introduce this survey by presenting the first measurement of the mass–metallicity relation (MZR) at high redshift in overdense environments via grism spectroscopy. From the completed MAMMOTH–Grism observations in the field of the BOSS1244 protocluster at
z
= 2.24 ± 0.02, we secure a sample of 36 protocluster member galaxies at
z
≈ 2.24, showing strong nebular emission lines (O
III
, H
β
, and O
II
) in their G141 spectra. Using the multi-wavelength broadband deep imaging from HST and ground-based telescopes, we measure their stellar masses in the range of 10
9
, 10
10.4
M
⊙
, instantaneous star formation rates (SFR) from 10 to 240
M
⊙
yr
−1
, and global gas-phase metallicities
1
3
,
1
of solar. Compared with similarly selected field-galaxy samples at the same redshift, our galaxies show, on average, increased SFRs by ∼0.06 dex and ∼0.18 dex at ∼10
10.1
M
⊙
and ∼10
9.8
M
⊙
, respectively. Using the stacked spectra of our sample galaxies, we derive the MZR in the BOSS1244 protocluster core as
12
+
log
(
O
/
H
)
=
0.136
±
0.018
×
log
(
M
*
/
M
⊙
)
+
7.082
±
0.175
, showing a significantly shallower slope than that in the field. This shallow MZR slope is likely caused by the combined effects of efficient recycling of feedback-driven winds and cold-mode gas accretion in protocluster environments. The former effect helps low-mass galaxies residing in overdensities retain their metal production, whereas the latter effect dilutes the metal content of high-mass galaxies, making them more metal-poor than their coeval field counterparts.
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