We present an analysis of , O iii88, N ii122, and far-infrared (FIR) fine-structure line observations obtained with Herschel/PACS, for ∼240 local luminous infrared galaxies (LIRGs) in the Great ...Observatories All-sky LIRG Survey. We find pronounced declines ("deficits") of line-to-FIR continuum emission for N ii122, , and as a function of FIR color and infrared luminosity surface density, . The median electron density of the ionized gas in LIRGs, based on the N ii122/N ii205 ratio, is = 41 cm−3. We find that the dispersion in the deficit of LIRGs is attributed to a varying fractional contribution of photodissociation regions (PDRs) to the observed emission, f( ) = / , which increases from ∼60% to ∼95% in the warmest LIRGs. The / ratio is tightly correlated with the PDR gas kinetic temperature in sources where is not optically thick or self-absorbed. For each galaxy, we derive the average PDR hydrogen density, , and intensity of the interstellar radiation field, G, in units of and find G/ ratios of ∼0.1-50 cm3, with ULIRGs populating the upper end of the distribution. There is a relation between G/ and , showing a critical break at 5 × 1010 L kpc−2. Below , G/ remains constant, 0.32 cm3, and variations in are driven by the number density of star-forming regions within a galaxy, with no change in their PDR properties. Above , G/ increases rapidly with , signaling a departure from the typical PDR conditions found in normal star-forming galaxies toward more intense/harder radiation fields and compact geometries typical of starbursting sources.
We present 3, 15, and 33 GHz imaging toward galaxy nuclei and extranuclear star-forming regions using the Karl G. Jansky Very Large Array as part of the Star Formation in Radio Survey. With 3-33 GHz ...radio spectra, we measured the spectral indices and corresponding thermal (free-free) emission fractions for a sample of 335 discrete regions having significant detections in at least two radio bands. After removing 14 likely background galaxies, we find that the median thermal fraction at 33 GHz is 92% 0.8% with a median absolute deviation of 11%, when a two-component power-law model is adopted to fit the radio spectrum. Limiting the sample to 238 sources that are confidently identified as star-forming regions and not affected by potential AGN contamination (i.e., having galactocentric radii rG ≥ 250 pc) results in a median thermal fraction of 93% 0.8% with a median absolute deviation of 10%. We further measure the thermal fraction at 33 GHz for 163 regions identified at 7″ resolution to be 94% 0.8% with a median absolute deviation of 8%. Together, these results confirm that free-free emission dominates the radio spectra of star-forming regions on scales up to ∼500 pc in normal star-forming galaxies. We additionally find a factor of ∼1.6 increase in the scatter of the measured spectral index and thermal fraction distributions as a function of decreasing galactocentric radius. This trend is likely reflective of the continuous star formation activity occurring in the galaxy centers, resulting in a larger contribution of diffuse nonthermal emission relative to star-forming regions in the disk.
ABSTRACT
The merger of two or more galaxies can enhance the inflow of material from galactic scales into the close environments of active galactic nuclei (AGNs), obscuring and feeding the ...supermassive black hole (SMBH). Both recent simulations and observations of AGN in mergers have confirmed that mergers are related to strong nuclear obscuration. However, it is still unclear how AGN obscuration evolves in the last phases of the merger process. We study a sample of 60 luminous and ultra-luminous IR galaxies (U/LIRGs) from the GOALS sample observed by NuSTAR. We find that the fraction of AGNs that are Compton thick (CT; $N_{\rm H}\ge 10^{24}\rm \, cm^{-2}$) peaks at $74_{-19}^{+14}{{\ \rm per\ cent}}$ at a late merger stage, prior to coalescence, when the nuclei have projected separations (dsep) of 0.4–6 kpc. A similar peak is also observed in the median NH $(1.6\pm 0.5)\times 10^{24}\rm \, cm^{-2}$. The vast majority ($85^{+7}_{-9}{{\ \rm per\ cent}}$) of the AGNs in the final merger stages (dsep ≲ 10 kpc) are heavily obscured ($N_{\rm H}\ge 10^{23}\rm \, cm^{-2}$), and the median NH of the accreting SMBHs in our sample is systematically higher than that of local hard X-ray-selected AGN, regardless of the merger stage. This implies that these objects have very obscured nuclear environments, with the $N_{\rm H}\ge 10^{23}\rm \, cm^{-2}$ gas almost completely covering the AGN in late mergers. CT AGNs tend to have systematically higher absorption-corrected X-ray luminosities than less obscured sources. This could either be due to an evolutionary effect, with more obscured sources accreting more rapidly because they have more gas available in their surroundings, or to a selection bias. The latter scenario would imply that we are still missing a large fraction of heavily obscured, lower luminosity ($L_{2-10}\lesssim 10^{43}\rm \, erg\, s^{-1}$) AGNs in U/LIRGs.
Abstract
We present the analysis of ∼100 pc scale compact radio continuum sources detected in 63 local (ultra)luminous infrared galaxies (U/LIRGs;
L
IR
≥ 10
11
L
⊙
), using FWHM ≲ 0.″1–0.″2 ...resolution 15 and 33 GHz observations with the Karl G. Jansky Very Large Array. We identify a total of 133 compact radio sources with effective radii of 8–170 pc, which are classified into four main categories—“AGN” (active galactic nuclei), “AGN/SBnuc” (AGN-starburst composite nucleus), “SBnuc” (starburst nucleus), and “SF” (star-forming clumps)—based on ancillary data sets and the literature. We find that “AGN” and “AGN/SBnuc” more frequently occur in late-stage mergers and have up to 3 dex higher 33 GHz luminosities and surface densities compared with “SBnuc” and “SF,” which may be attributed to extreme nuclear starburst and/or AGN activity in the former. Star formation rates (SFRs) and surface densities (Σ
SFR
) are measured for “SF” and “SBnuc” using both the total 33 GHz continuum emission (SFR ∼ 0.14–13
M
⊙
yr
−1
, Σ
SFR
∼ 13–1600
M
⊙
yr
−1
kpc
−2
) and the thermal free–free emission from H
ii
regions (median SFR
th
∼ 0.4
M
⊙
yr
−1
,
Σ
SFR
th
∼
44
M
⊙
yr
−1
kpc
−2
). These values are 1–2 dex higher than those measured for similar-sized clumps in nearby normal (non-U/LIRGs). The latter also have a much flatter median 15–33 GHz spectral index (∼−0.08) compared with “SBnuc” and “SF” (∼−0.46), which may reflect higher nonthermal contribution from supernovae and/or interstellar medium densities in local U/LIRGs that directly result from and/or lead to their extreme star-forming activities on 100 pc scales.
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•Cell-free transcription and translation systems are used for testing and facilitating the implementation of novel circuits in cells.•Cell-free transcription and translation systems ...can be encapsulated in microcompartments.•Microcompartments are used to study gene expression in a physicochemical environment and at a scale close to those of the cell.•Microcompartments are capable of communication with cells and other artificial cells and can be used to prototype novel communication channels.
Recent efforts in synthetic biology have shown the possibility of engineering distributed functions in populations of living cells, which requires the development of highly orthogonal, genetically encoded communication pathways. Cell-free transcription-translation (TXTL) reactions encapsulated in microcompartments enable prototyping of molecular communication channels and their integration into engineered genetic circuits by mimicking critical cell features, such as gene expression, cell size, and cell individuality within a community. In this review, we discuss the uses of cell-free transcription–translation reactions for the development of synthetic genetic circuits, with a special focus on the use of microcompartments supporting this reaction. We highlight several studies where molecular communication between non-living microcompartments and living cells have been successfully engineered.
Abstract
Cell-free protein synthesis has been widely used as a “breadboard” for design of synthetic genetic networks. However, due to a severe lack of modularity, forward engineering of genetic ...networks remains challenging. Here, we demonstrate how a combination of optimal experimental design and microfluidics allows us to devise dynamic cell-free gene expression experiments providing maximum information content for subsequent non-linear model identification. Importantly, we reveal that applying this methodology to a library of genetic circuits, that share common elements, further increases the information content of the data resulting in higher accuracy of model parameters. To show modularity of model parameters, we design a pulse decoder and bistable switch, and predict their behaviour both qualitatively and quantitatively. Finally, we update the parameter database and indicate that network topology affects parameter estimation accuracy. Utilizing our methodology provides us with more accurate model parameters, a necessity for forward engineering of complex genetic networks.
We present HST narrowband near-infrared imaging of Pa and Paβ emission of 48 local luminous infrared galaxies (LIRGs) from the Great Observatories All-Sky LIRG Survey. These data allow us to measure ...the properties of 810 spatially resolved star-forming regions (59 nuclei and 751 extranuclear clumps) and directly compare their properties to those found in both local and high-redshift star-forming galaxies. We find that in LIRGs the star-forming clumps have radii ranging from ∼90 to 900 pc and star formation rates (SFRs) of ∼1 × 10−3 to 10 M yr−1, with median values for extranuclear clumps of 170 pc and 0.03 M yr−1. The detected star-forming clumps are young, with a median stellar age of 8.7 Myr, and have a median stellar mass of 5 × 105 M . The SFRs span the range of those found in normal local star-forming galaxies to those found in high-redshift star-forming galaxies at z = 1-3. The luminosity function of the LIRG clumps has a flatter slope than found in lower-luminosity, star-forming galaxies, indicating a relative excess of luminous star-forming clumps. In order to predict the possible range of star-forming histories and gas fractions, we compare the star-forming clumps to those measured in the MassiveFIRE high-resolution cosmological simulation. The star-forming clumps in MassiveFIRE cover the same range of SFRs and sizes found in the local LIRGs and have total gas fractions that extend from 10% to 90%. If local LIRGs are similar to these simulated galaxies, we expect that future observations with ALMA will find a large range of gas fractions, and corresponding star formation efficiencies, among the star-forming clumps in LIRGs.
Abstract
We present the results of a Hubble Space Telescope WFC3 near-UV and Advanced Camera for Surveys Wide Field Channel optical study into the star cluster populations of a sample of 10 luminous ...infrared galaxies (LIRGs) in the Great Observatories All-Sky LIRG Survey. Through integrated broadband photometry we have derived ages, masses, and extinctions for a total of 1027 star clusters in galaxies with
d
L
< 110 Mpc in order to avoid issues related to cluster bending. The measured cluster age distribution slope of
dN
/
d
τ
∝
τ
−
0.5
+
/
−
0.12
is steeper than what has been observed in lower-luminosity star-forming galaxies. Further, differences in the slope of the observed cluster age distribution between inner- (
dN
/
d
τ
∝
τ
−
1.07
+
/
−
0.12
) and outer-disk (
dN
/
d
τ
∝
τ
−
0.37
+
/
−
0.09
) star clusters provide evidence of mass-dependent cluster destruction in the central regions of LIRGs driven primarily by the combined effect of strong tidal shocks and encounters with massive giant molecular clouds. Excluding the nuclear ring surrounding the Seyfert 1 nucleus in NGC 7469, the derived cluster mass function (CMF;
dN
/
dM
∝
M
α
) offers marginal evidence for a truncation in the power law at
M
t
∼ 2×10
6
M
⊙
for our three most
cluster-rich
sources, which are all classified as early stage mergers. Finally, we find evidence of a flattening of the CMF slope of
dN
/
dM
∝
M
−
1.42
±
0.1
for clusters in late-stage mergers relative to early stage (
α
= −1.65 ± 0.02), which we attribute to an increase in the formation of massive clusters over the course of the interaction.
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