24 research outputs found
Intensity mapping of [CII] from early galaxies
The intensity mapping of the [CII] 157.7 m fine-structure emission
line represents an ideal experiment to probe star formation activity in
galaxies, especially in those that are too faint to be individually detected.
Here, we investigate the feasibility of such an experiment for
galaxies. We construct the relation from observations
and simulations, then generate mock [CII] intensity maps by applying this
relation to halo catalogs built from large scale N-body simulations. Maps of
the extragalactic far-infrared (FIR) continuum, referred to as "foreground",
and CO rotational transition lines and [CI] fine-structure lines referred to as
"contamination", are produced as well. We find that, at 316 GHz (corresponding
to ), the mean intensities of the extragalactic FIR continuum,
[CII] signal, all CO lines from to 13 and two [CI] lines are Jy sr, Jy sr, Jy sr
and Jy sr, respectively. We discuss a method that allows us
to subtract the FIR continuum foreground by removing a spectrally smooth
component from each line of sight, and to suppress the CO/[CI] contamination by
discarding pixels that are bright in contamination emission. The [CII]
signal comes mainly from halos in the mass range ; as
this mass range is narrow, intensity mapping is an ideal experiment to
investigate these early galaxies. In principle such signal is accessible to a
ground-based telescope with a 6 m aperture, 150 K system temperature, a
pixels FIR camera in 5000 hr total integration time, however it
is difficult to perform such an experiment by using currently available
telescopes.Comment: 12 pages, 10 figures. Accepted for publication in MNRA
Molecular clumps photoevaporation in ionized regions
We study the photoevaporation of molecular clumps exposed to a UV radiation
field including hydrogen-ionizing photons ( eV) produced by
massive stars or quasars. We follow the propagation and collision of shock
waves inside clumps and take into account self-shielding effects, determining
the evolution of clump size and density with time. The structure of the
ionization-photodissociation region (iPDR) is obtained for different initial
clump masses () and impinging fluxes ( in units of the Habing flux). The cases of molecular clumps engulfed in
the HII region of an OB star and clumps carried within quasar outflows are
treated separately. We find that the clump undergoes in both cases an initial
shock-contraction phase and a following expansion phase, which lets the
radiation penetrate in until the clump is completely evaporated. Typical
evaporation time-scales are Myr in the stellar case and 0.1 Myr
in the quasar case, where the clump mass is 0.1 and respectively. We find that clump lifetimes in quasar outflows are
compatible with their observed extension, suggesting that photoevaporation is
the main mechanism regulating the size of molecular outflows.Comment: 13 pages, 12 figures, accepted for publication in MNRA
Ly{\alpha} emission from galaxies in the Epoch of Reionization
The intrinsic strength of the Ly line in young, star-forming systems
makes it a special tool for studying high-redshift galaxies. However,
interpreting observations remains challenging due to the complex radiative
transfer involved. Here, we combine state-of-the-art hydrodynamical simulations
of 'Althaea', a prototypical Lyman Break Galaxy (LBG, stellar mass
at , with detailed
radiative transfer computations of dust/continuum, [CII] 158 m, and
Ly to clarify the relation between the galaxy properties and its
Ly emission. Althaea exhibits low () Ly escape
fractions and Equivalent Widths, EW Angstrom for the simulated
lines of sight, with a large scatter. The correlation between escape fraction
and inclination is weak, as a result of the rather chaotic structure of
high-redshift galaxies. Low values persist even if we artificially
remove neutral gas around star forming regions to mimick the presence of HII
regions. The high attenuation is primarily caused by dust clumps co-located
with young stellar clusters. We can turn Althaea into a Lyman Alpha Emitter
(LAE) only if we artificially remove dust from the clumps, yielding EWs up to
Angstrom. Our study suggests that the LBG-LAE duty-cycle required by
recent clustering measurements poses the challenging problem of a dynamically
changing dust attenuation. Finally, we find an anti-correlation between the
magnitude of Ly-[CII] line velocity shift and Ly luminosity.Comment: published in MNRA
A methodology to select galaxies just after the quenching of star formation
We propose a new methodology aimed at finding star-forming galaxies in the
phase which immediately follows the star-formation (SF) quenching, based on the
use of high- to low-ionization emission line ratios. These ratios rapidly
disappear after the SF halt, due to the softening of the UV ionizing radiation.
We focus on [O III] 5007/H and [Ne III] 3869/[O II]
3727, studying them with simulations obtained with the CLOUDY
photoionization code. If a sharp quenching is assumed, we find that the two
ratios are very sensitive tracers as they drop by a factor 10 within
10 Myr from the interruption of the SF; instead, if a smoother and
slower SF decline is assumed (i.e. an exponentially declining star-formation
history with -folding time 200 Myr), they decrease by a factor
2 within 80 Myr. We mitigate the ionization -- metallicity
degeneracy affecting our methodology using pairs of emission line ratios
separately related to metallicity and ionization, adopting the [N II]
6584/[O II] 3727 ratio as metallicity diagnostic. Using a
Sloan Digital Sky Survey galaxy sample, we identify 10 examples among the most
extreme quenching candidates within the [O III] 5007/H vs. [N
II] 6584/[O II] 3727 plane, characterized by low [O III]
5007/H, faint [Ne III] 3869, and by blue
dust-corrected spectra and colours, as expected if the SF quenching has
occurred in the very recent past. Our results also suggest that the observed
fractions of quenching candidates can be used to constrain the quenching
mechanism at work and its time-scales.Comment: Accepted for publication in MNRAS; 19 pages, 21 figures, 1 tabl
Spatially resolved Kennicutt-Schmidt relation at z ≈ 7 and its connection with the interstellar medium properties
We exploit moderately resolved [O III], [C II] and dust continuum ALMA observations to derive the gas density (n), the gas-phase metallicity (Z) and the deviation from the Kennicutt-Schmidt (KS) relation (κs) on ≈sub−kpc
scales in the interstellar medium (ISM) of five bright Lyman Break Galaxies at the Epoch of Reionization (z ≈ 7). To do so, we use GLAM, a state-of-art, physically motivated Bayesian model that links the [C II]and [O III] surface brightness (Σ[CII], Σ[OIII]) and the SFR surface density (ΣSFR) to n, κs, and Z. All five sources are characterized by a central starbursting region, where the Σgas vs ΣSFR align ≈10 × above the KS relation (κs ≈ 10). This translates into gas depletion times in the range tdep ≈ 80 − 250 Myr. The inner starbursting centers are characterized by higher gas density (log (n/cm−3) ≈ 2.5 − 3.0) and higher metallicity (log (Z/Z⊙) ≈ −0.5) than the galaxy outskirts. We derive marginally negative radial metallicity gradients (∇log Z ≈ −0.03 ± 0.07 dex/kpc), and a dust temperature (Td ≈ 32 − 38 K) that anticorrelates with the gas depletion time
AGN impact on the molecular gas in galactic centers as probed by CO lines
We present a detailed analysis of the X-ray, infrared, and carbon monoxide
(CO) emission for a sample of 35 local (), active ( erg s) galaxies. Our goal is to infer the contribution of
far-ultraviolet (FUV) radiation from star formation (SF), and X-ray radiation
from the active galactic nuclei (AGN), respectively producing photodissociation
regions (PDRs) and X-ray dominated regions (XDRs), to the molecular gas
heating. To this aim, we exploit the CO spectral line energy distribution (CO
SLED) as traced by Herschel, complemented with data from single-dish telescopes
for the low-J lines, and high-resolution ALMA images of the mid-J CO emitting
region. By comparing our results to the Schmidt-Kennicutt relation, we find no
evidence for AGN influence on the cold and low-density gas on kpc-scales. On
nuclear (r = 250 pc) scales, we find weak correlations between the CO line
ratios and either the FUV or X-ray fluxes: this may indicate that neither SF
nor AGN radiation dominates the gas excitation, at least at r = 250 pc. From a
comparison of the CO line ratios with PDR and XDR models, we find that PDRs can
reproduce observations only in presence of extremely high gas densities ( cm). In the XDR case, instead, the models suggest moderate
densities ( cm). We conclude that a mix of the two
mechanisms (PDR for the mid-J, XDR or possibly shocks for the high-J) is
necessary to explain the observed CO excitation in active galaxies
Large Population of ALMA Galaxies at z>6 with Very High [OIII]88um to [CII]158um Flux Ratios: Evidence of Extremely High Ionization Parameter or PDR Deficit?
We present our new ALMA observations targeting [OIII]88um, [CII]158um,
[NII]122um, and dust continuum emission for three Lyman break galaxies at
z=6.0293-6.2037 identified in the Subaru/Hyper Suprime-Cam survey. We clearly
detect [OIII] and [CII] lines from all of the galaxies at 4.3-11.8sigma levels,
and identify multi-band dust continuum emission in two of the three galaxies,
allowing us to estimate infrared luminosities and dust temperatures
simultaneously. In conjunction with previous ALMA observations for six galaxies
at z>6, we confirm that all the nine z=6-9 galaxies have high [OIII]/[CII]
ratios of L[OIII]/L[CII]~3-20, ~10 times higher than z~0 galaxies. We also find
a positive correlation between the [OIII]/[CII] ratio and the Lya equivalent
width (EW) at the ~90% confidence level. We carefully investigate physical
origins of the high [OIII]/[CII] ratios at z=6-9 using Cloudy, and find that
high density of the interstellar medium, low C/O abundance ratio, and the
cosmic microwave background attenuation are responsible to only a part of the
z=6-9 galaxies. Instead, the observed high [OIII]/[CII] ratios are explained by
10-100 times higher ionization parameters or low photodissociation region (PDR)
covering fractions of 0-10%, both of which are consistent with our [NII]
observations. The latter scenario can be reproduced with a density bounded
nebula with PDR deficit, which would enhance the Lya, Lyman continuum, and C+
ionizing photons escape from galaxies, consistent with the [OIII]/[CII]-Lya EW
correlation we find.Comment: 20 pages, 18 figures, Accepted for publication in Ap
ALMA Observations for CO Emission from Luminous Lyman-break Galaxies at -
We present our new Atacama Large Millimeter/submillimeter Array (ALMA)
observations targeting CO(6-5) emission from three luminous Lyman break
galaxies (LBGs) at - found in the Subaru/Hyper
Suprime-Cam survey, whose [OIII]m and [CII]m emission have been
detected with ALMA. We find a marginal detection of the CO(6-5) line from one
of our LBGs, J0235-0532, at the significance level and obtain
upper limits for the other two LBGs, J1211-0118 and J0217-0208. Our
luminous LBGs are consistent with the previously found correlation between the
CO luminosity and the infrared luminosity. The unique ensemble of the multiple
far-infrared emission lines and underlying continuum fed to a photodissociation
region model reveal that J0235-0532 has a relatively high hydrogen nucleus
density that is comparable to those of low- (U)LIRGs, quasars, and Galactic
star-forming regions with high values, while the other two LBGs
have lower consistent with local star-forming galaxies. By
carefully taking account of various uncertainties, we obtain total gas mass and
gas surface density constraints from their CO luminosity measurements. We find
that J0235-0532 locates below the Kennicutt-Schmidt (KS) relation, comparable
to the previously CO(2-1) detected LBG, HZ10. Combined with previous
results for dusty starbursts at similar redshifts, the KS relation at -
is on average consistent with the local one.Comment: 33 pages, 12 figures, accepted for publication in Ap
Molecular hydrogen in Lyman Alpha Emitters
We present a physically motivated model to estimate the molecular hydrogen
(H2) content of high-redshift (z~5.7,6.6) Lyman Alpha Emitters (LAEs) extracted
from a suite of cosmological simulations. We find that the H2 mass fraction,
(f_H2), depends on three main LAE physical properties: (a) star formation rate,
(b) dust mass, and (c) cold neutral gas mass. At z~5.7, the value of f_H2 peaks
and ranges between 0.5-0.9 for intermediate mass LAEs with stellar mass M_* ~
10^{9-10} solar mass, decreasing for both smaller and larger galaxies. However,
the largest value of the H2 mass is found in the most luminous LAEs. These
trends also hold at z\sim6.6, although, due to a lower dust content,
f_H2(z=6.6)\sim0.5 f_H2(z=5.7) when averaged over all LAEs; they arise due to
the interplay between the H2 formation/shielding controlled by dust and the
intensity of the ultraviolet (UV) Lyman-Werner photo-dissociating radiation
produced by stars. We then predict the carbon monoxide (CO) luminosities for
such LAEs and check that they are consistent with the upper limits found by
Wagg et al. (2009) for two z>6 LAEs. At z\sim(5.7, 6.6), the lowest CO
rotational transition observable for both samples with the actual capabilities
of Atacama Large Millimeter Array (ALMA) is the CO(6-5). We find that at
z\sim5.7, about 1-2% of LAEs, i.e., those with an observed Lyman Alpha
luminosity larger than 10^{43.2} erg/s would be detectable with an integration
time of 5-10 hours (S/N=5); at z\sim6.6 none of the LAEs would be detectable in
CO, even with an ALMA integration time of 10 hours. We also build the CO `flux
function', i.e., the number density of LAEs as a function of the
line-integrated CO flux, S_CO, and show that it peaks at S_CO = 0.1 mJy at
z\sim5.7, progressively shifting to lower values at higher redshifts. We end by
discussing the model uncertainties.Comment: Accepted for publication in MNRA