arXiv subjects

Nia Imara

Publications and source records attributed to Nia Imara.

23 records · Page 2Linked to original sources

arXiv2016

The HI Probability Distribution Function and the Atomic-to-Molecular Transition in Molecular Clouds

We characterize the column density probability distributions functions (PDFs) of the atomic hydrogen gas, HI, associated with seven Galactic molecular clouds (MCs). We use 21 cm observations from the Leiden/Argentine/Bonn Galactic HI Survey to derive column density maps and PDFs. We find that the peaks of the HI PDFs occur at column densities ranging from ~1-2$\times 10^{21}$ cm$^2$ (equivalently, ~0.5-1 mag). The PDFs are uniformly narrow, with a mean dispersion of $σ_{HI}\approx 10^{20}$ cm$^2$ (~0.1 mag). We also investigate the HI-to-H$_2$ transition towards the cloud complexes and estimate HI surface densities ranging from 7-16 $M_\odot$ pc$^{-2}$ at the transition. We propose that the HI PDF is a fitting tool for identifying the HI-to-H$_2$ transition column in Galactic MCs.

astro-ph.GA↗

arXiv2016

The Distortion of the Cosmic Microwave Background Spectrum Due to Intergalactic Dust

Infrared emission from intergalactic dust might compromise the ability of future experiments to detect subtle spectral distortions in the Cosmic Microwave Background (CMB) from the early Universe. We provide the first estimate of foreground contamination of the CMB signal due to diffuse dust emission in the intergalactic medium. We use models of the extragalactic background light to calculate the intensity of intergalactic dust emission and find that emission by intergalactic dust at redshifts z<0.5 exceeds the sensitivity of the planned Primordial Inflation Explorer (PIXIE) to CMB spectral distortions by 1-3 orders of magnitude. We place an upper limit of 0.23% on the contribution to the far-infrared background from intergalactic dust emission.

astro-ph.CO↗

arXiv2015

Limits on Intergalactic Dust During Reionization

In this Letter, we constrain the dust-to-gas ratio in the intergalactic medium (IGM) at high redshifts. We employ models for dust in the local Universe to contrain the dust-to-gas ratio during the epoch of reionization at redshifts z ~ 6-10. The observed level of reddening of high redshift galaxies implies that the IGM was enriched to an intergalactic dust-to-gas ratio of less than 3% of the Milky Way value by a redshift of z=10.

astro-ph.CO↗

arXiv2015

Rethinking a Mysterious Molecular Cloud

I present high-resolution column density maps of two molecular clouds having strikingly different star formation rates. To better understand the unusual, massive G216-2.5, a molecular cloud with no massive star formation, the distribution of its molecular gas is compared to that of the Rosette Molecular Cloud. Far-infrared data from Herschel are used to derive $N(\mathrm{H}_2)$ maps of each cloud and are combined with $I_{\mathrm{CO}}$ data to determine the CO-to-H$_2$ ratio, $X_{\mathrm{CO}}$. In addition, the probability distribution functions (PDFs) and cumulative mass fractions of the clouds are compared. For G216-2.5, $< N(\mathrm{H}_2) >=7.8\times 10^{20} cm^{-2}$ and $< X_{\mathrm{CO}} > =2.2\times 10^{20} (K km s^{-1})^{-1}$; for the Rosette, $< N(\mathrm{H}_2) > =1.8\times 10^{21} cm^{-2}$ and $ < X_{\mathrm{CO}} > =2.8\times 10^{20} (K km s^{-1})^{-1}$. The PDFs of both clouds are log-normal for extinctions below $\sim 2$ mag and both show departures from log-normality at high extinctions. Although it is the less-massive cloud, the Rosette has a higher fraction of its mass in the form of dense gas and contains $1389 M_\odot$ of gas above the so-called extinction threshold for star formation, $A_V = 7.3$ mag. The G216-2.5 cloud has $874 M_\odot$ of dense gas above this threshold.

astro-ph.SR↗

arXiv2007

Extinction in the Large Magellanic Cloud

We present an extinction map of the Large Magellanic Cloud (LMC), using 204,502 stars from the Two Micron All Sky Survey point source catalog. We first use the NICE method to determine the reddening distribution, \ehk and \ejh, which we compare to the HI distribution to find a near-infrared reddening law of $\ejh/\ehk=1.20\pm 0.04$. A visual extinction map ($\sim 6^\circ\times 6^\circ$) of the LMC is created using the NICER method; at 4 arcmin resolution, a mean value of $\av=0.38$ mag is found. We derive the LMC CO-to-H$_2$ conversion factor, $\x{LMC}$, independent of assumptions about the virialization of giant molecular clouds, by comparing the NICER extinction map with NANTEN $^{12}$CO observations. In regions where $\av>1$ mag and $^{12}$CO emission is $\ge$ 2 \counits, we measure $\x{LMC}=9.3\pm 0.4\times 10^{20} \xunits$. In the same regions, the LMC contains a total molecular mass of $(4.5\pm 0.2)\times 10^7 \msun$.

astro-ph↗