arXiv subjects

Jonathan V. Smoker

Publications and source records attributed to Jonathan V. Smoker.

5 recordsLinked to original sources

arXiv2025

Mapping the diffuse interstellar bands $λ$5780 and $λ$6284 in the luminous infrared galaxy merger NGC 6240

[ABRIDGED] DIBs are faint absorption features of mainly unknown origin. Observational constraints on their carriers have been provided in the vast majority of the cases via observations in our Galaxy. Detections in other galaxies are scarce. However, they can further constrain the nature of the carriers by sampling different environments and they can put into test the ubiquity of the molecules creating these features. Using the MUSE data of the LIRG NGC 6240, we mapped the DIB5780 over an almost contiguous area of ~76.96 kpc^2 in the center of the system. We also traced the DIBl6284 over two separate areas toward the north and south of the system, with an extent of ~21.22 kpc^2 and ~31.41 kpc^2 (with a total detected area of ~59.78 kpc^2). This is the first time that the l6284 DIB has been mapped outside our Galaxy. Both maps were compared with the attenuation on the overall stellar population and the ionised gas. Both DIBs are detected in locations with high attenuation (E(B-V)_Gas} > 0.3 and E(B-V)_Stellar >0.1), supporting the connection between DIB carriers and dust. Moreover, when compared with other galaxies, DIBs correlate better with stellar than with the ionised gas attenuation. The DIBl6284 presents a stronger correlation with reddening than the l5780 DIB does that can be attributed to a different nature of the carriers causing these DIBs, or a combined effect of a dependency with the metallicity and the different locations where these DIBs have been measured. In addition, we show that NaI D strongly correlates with both DIBs and advocate the usage of DIBs as a first order tracer for amount of material, in the case where NaI D reaches saturation. The findings here show that DIB carriers can exist and survive in an environment as extreme as a galaxy hosting AGN and allow to envision the possibilities integral field spectrographs have to study DIBs well beyond our Galaxy.

astro-ph.GA↗

arXiv2018

The EDIBLES survey IV. Cosmic ray ionization rates in diffuse clouds from near-ultraviolet observations of interstellar OH$^+$

We report cosmic ray ionization rates towards ten reddened stars studied within the framework of the EDIBLES (ESO Diffuse Interstellar Bands Large Exploration Survey) program, using the VLT-UVES. For each sightline, between 2 and 10 individual rotational lines of OH$^+$ have been detected in its (0,0) and (1,0) $A^3Π-X^3Σ^-$ electronic band system. This allows constraining of OH$^+$ column densities towards different objects. Results are also presented for 28 additional sightlines for which only one or rather weak signals are found. An analysis of these data makes it possible to derive the primary cosmic ray ionization rate $ζ_p$ in the targeted diffuse interstellar clouds. For the ten selected targets, we obtain a range of values for $ζ_p$ equal to $(3.9-16.4) \times 10^{-16}~\mathrm{s}^{-1}$. These values are higher than the numbers derived in previous detections of interstellar OH$^+$ in the far-infrared / sub-millimeter-wave regions and in other near-ultraviolet studies. This difference is a result of using new OH$^+$ oscillator strength values and a more complete picture of all relevant OH$^+$ formation and destruction routes (including the effect of proton recombinations on PAHs), and the relatively high $N$(OH$^+$) seen toward those ten targets.

astro-ph.GA↗

arXiv2017

The Origin of B-Type Runaway Stars: Non-LTE Abundances as a Diagnostic

There are two accepted mechanisms to explain the origin of runaway OB-type stars: the Binary Supernova Scenario (BSS), and the Cluster Ejection Scenario (CES). In the former, a supernova explosion within a close binary ejects the secondary star, while in the latter close multi-body interactions in a dense cluster cause one or more of the stars to be ejected from the region at high velocity. Both mechanisms have the potential to affect the surface composition of the runaway star. TLUSTY non-LTE model atmosphere calculations have been used to determine atmospheric parameters and carbon, nitrogen, magnesium and silicon abundances for a sample of B-type runaways. These same analytical tools were used by Hunter et al. (2009) for their analysis of 50 B-type open cluster Galactic stars (i.e. non-runaways). Effective temperatures were deduced using the silicon-ionization balance technique, surface gravities from Balmer line profiles and microturbulent velocities derived using the Si spectrum. The runaways show no obvious abundance anomalies when compared with stars in the open clusters. The runaways do show a spread in composition which almost certainly reflects the Galactic abundance gradient and a range in the birthplaces of the runaways in the Galactic disk. Since the observed Galactic abundance gradients of C, N, Mg and Si are of a similar magnitude, the abundance ratios (e.g., N/Mg) are, as obtained, essentially uniform across the sample.

astro-ph.SR↗

arXiv2015

Early-type stars observed in the ESO UVES Paranal Observatory Project - V. Time-variable interstellar absorption

The structure and properties of the diffuse interstellar medium (ISM) on small scales, sub-au to 1 pc, are poorly understood. We compare interstellar absorption-lines, observed towards a selection of O- and B-type stars at two or more epochs, to search for variations over time caused by the transverse motion of each star combined with changes in the structure in the foreground ISM. Two sets of data were used: 83 VLT- UVES spectra with approximately 6 yr between epochs and 21 McDonald observatory 2.7m telescope echelle spectra with 6 - 20 yr between epochs, over a range of scales from 0 - 360 au. The interstellar absorption-lines observed at the two epochs were subtracted and searched for any residuals due to changes in the foreground ISM. Of the 104 sightlines investigated with typically five or more components in Na I D, possible temporal variation was identified in five UVES spectra (six components), in Ca II, Ca I and/or Na I absorption-lines. The variations detected range from 7\% to a factor of 3.6 in column density. No variation was found in any other interstellar species. Most sightlines show no variation, with 3σ upper limits to changes of the order 0.1 - 0.3 dex in Ca II and Na I. These variations observed imply that fine-scale structure is present in the ISM, but at the resolution available in this study, is not very common at visible wavelengths. A determination of the electron densities and lower limits to the total number density of a sample of the sightlines implies that there is no striking difference between these parameters in sightlines with, and sightlines without, varying components.

astro-ph.SR↗

arXiv2010

Exploring the Origin and Fate of the Magellanic Stream with Ultraviolet and Optical Absorption

(Abridged) We present an analysis of ionization and metal enrichment in the Magellanic Stream (MS), the nearest gaseous tidal stream, using HST/STIS and FUSE ultraviolet spectroscopy of two background AGN, NGC 7469 and Mrk 335. For NGC 7469, we include optical spectroscopy from VLT/UVES. In both sightlines the MS is detected in low-ion and high-ion absorption. Toward NGC 7469, we measure a MS oxygen abundance [O/H]_MS=[OI/HI]=-1.00+/-0.05(stat)+/-0.08(syst), supporting the view that the Stream originates in the SMC rather than the LMC. We use CLOUDY to model the low-ion phase of the Stream as a photoionized plasma using the observed Si III/Si II and C III/C II ratios. Toward Mrk 335 this yields an ionization parameter log U between -3.45 and -3.15 and a gas density log (n_H/cm^-3) between -2.51 and -2.21. Toward NGC 7469 we derive sub-solar abundance ratios for [Si/O], [Fe/O], and [Al/O], indicating the presence of dust in the MS. The high-ion column densities are too large to be explained by photoionization, but also cannot be explained by a single-temperature collisional-ionization model (equilibrium or non-equilibrium). This suggests the high-ion plasma is multi-phase. Summing over the low-ion and high-ion phases, we derive conservative lower limits on the ratio N(total H II)/N(H I) of >19 toward NGC 7469 and >330 toward Mrk 335, showing that along these two directions the vast majority of the Stream has been ionized. The presence of warm-hot plasma together with the small-scale structure observed at 21 cm provides evidence for an evaporative interaction with the hot Galactic corona. This scenario, predicted by hydrodynamical simulations, suggests that the fate of the MS will be to replenish the Galactic corona with new plasma, rather than to bring neutral fuel to the disk.

astro-ph.GA↗