Mapping atomic and diffuse interstellar band absorption across the Magellanic Clouds and the Milky Way

Bailey, Mandy; Loon, Jacco Th. van; Sarre, P. J.; Beckman, J. E.

doi:10.1093/mnras/stv2178

Cited by 22 publications

(31 citation statements)

References 46 publications

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“…Those overall environmental factors are likely to have similar effects on the abundances of each trace species, however, so that their ratios (N(X I)/N(Y I)) might not differ much from the typical Galactic values. (The abundances of CH, H 2 , and the [unknown] carriers of the diffuse interstellar bands appear to have a more complex behavior in the Magellanic Clouds-with dependences on those global factors, on consequent differences in cloud structure, and also on local physical conditions; Tumlinson et al 2002;Cox et al , 2007Cox & Spaans 2006;Welty et al 2006Welty et al , 2012Welty et al , 2013van Loon et al 2013;Bailey et al 2015; see also Vos et al 2011. ) The plots in Figure 3 indicate that our seven Magellanic Cloud sight lines do agree well with the Galactic trends for N (C I tot ) versus N(Na I) and N(CH), but that they fall slightly below the Galactic trends for N(C I tot ) versus N(K I) and N (H 2 ).…”

Section: Abundance and Behavior Of CImentioning

confidence: 99%

Thermal Pressures in the Interstellar Medium of the Magellanic Clouds*

Welty

Lauroesch

Wong

et al. 2016

ApJ

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We discuss the thermal pressures (n H T) in predominantly cold, neutral interstellar gas in the Magellanic Clouds, derived from analyses of the fine-structure excitation of neutral carbon, as seen in high-resolution Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra of seven diverse sight lines in the LMC and SMC. Detailed fits to the line profiles of the absorption from C I, C I * , and C I ** yield consistent column densities for the three to six C I multiplets detected in each sight line. In the LMC and SMC, N(C I tot ) is consistent with Galactic trends versus N(Na I) and N(CH), but is slightly lower versus N(K I) and N(H 2 ). As for N(Na I) and N(K I), N(C I tot ) is generally significantly lower, for a given N(H tot ), in the LMC and (especially) in the SMC, compared to the local Galactic relationship. For the LMC and SMC components with well-determined column densities for C I, C I * , and C I ** , the derived thermal pressures are typically factors of a few higher than the values found for most cold, neutral clouds in the Galactic ISM. Such differences are consistent with the predictions of models for clouds in systems (like the LMC and SMC) that are characterized by lower metallicities, lower dust-to-gas ratios, and enhanced radiation fields-where higher pressures are required for stable cold, neutral clouds. The pressures may be further enhanced by energetic activity (e.g., due to stellar winds, star formation, and/or supernova remnants) in several of the regions probed by these sight lines. Comparisons are made with the C I observed in some quasar absorption-line systems.

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Section: Abundance and Behavior Of CImentioning

confidence: 99%

Thermal Pressures in the Interstellar Medium of the Magellanic Clouds*

Welty

Lauroesch

Wong

et al. 2016

ApJ

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“…Two issues were encountered during data processing: bias instability and wavelength calibration offsets (for more details see Bailey 2014). The fast read-out mode makes use of two amplifiers, resulting in different bias levels for both halves of the detector.…”

Section: Data Processingmentioning

confidence: 99%

“…In these projections, there is a clear gap which corresponds to the northern hemisphere which is covered in Papers II and III. Also indicated are the directions towards the Magellanic Clouds, which have been studied in the past (e.g., Cox et al 2006;van Loon et al 2013) and is the subject of a large DIB survey presented in Bailey et al (2015).…”

Section: Mapsmentioning

confidence: 99%

“…Also, by probing very local interstellar matter the sight lines suffer less from overlapping cloud structures, so the behaviour of the various tracers may be simpler to interpret and more telling. DIBs have been used successfully to map extra-planar gas (van Loon et al 2009;Baron et al 2015) and the Magellanic Clouds (van Loon et al 2013;Bailey et al 2015), as well as parts of the Milky Way (Kos et al 2014;Zasowski et al 2015). The elusiveness of the gas within the Local Bubble, however, requires very low noise levels on the measurements and thus calls for dedicated observations.…”

Section: Introductionmentioning

confidence: 99%

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Probing the Local Bubble with diffuse interstellar bands

Bailey

Loon

Farhang

et al. 2015

A&A

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Context. The Sun traverses a low-density, hot entity called the Local Bubble. Despite its relevance to life on Earth, the conditions in the Local Bubble and its exact configuration are not very well known. Besides that, there is some unknown interstellar substance that causes a host of absorption bands across the optical spectrum, called diffuse interstellar bands (DIBs). Aims. We have started a project to chart the Local Bubble in a novel way and learn more about the carriers of the DIBs, by using DIBs as tracers of diffuse gas and environmental conditions. Methods. We conducted a high signal-to-noise spectroscopic survey of 670 nearby early-type stars to map DIB absorption in and around the Local Bubble. The project started with a southern hemisphere survey conducted at the European Southern Observatory's New Technology Telescope and has since been extended to an all-sky survey using the Isaac Newton Telescope. Results. In this first paper in the series, we introduce the overall project and present the results from the southern hemisphere survey. We make available a catalogue of equivalent-width measurements of the DIBs at 5780, 5797, 5850, 6196, 6203, 6270, 6283, and 6614 Å, of the interstellar Na i D lines at 5890 and 5896 Å, and of the stellar He i line at 5876 Å. We find that the 5780 Å DIB is relatively strong throughout, as compared to the 5797 Å DIB, but especially within the Local Bubble and at the interface with a more neutral medium. The 6203 Å DIB shows similar behaviour with respect to the 6196 Å DIB. Some nearby stars show surprisingly strong DIBs, whereas some distant stars show very weak DIBs, indicating small-scale structure within, as well as outside, the Local Bubble. The sight lines with non-detections trace the extent of the Local Bubble especially clearly and show it opening out into the halo. Conclusions. The Local Bubble has a wall that is in contact with hot gas and/or a harsh interstellar radiation field. That wall is perforated, though, causing leakage of radiation and possibly hot gas. On the other hand, compact self-shielded cloudlets are present much closer to the Sun, probably within the Local Bubble itself. As for the carriers of the DIBs, our observations confirm the notion that these are large molecules whose differences in behaviour are mainly governed by their differing resilience and/or electrical charge, with more subtle differences possibly related to varying excitation.

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“…Nowadays, there are certainly many more DIB detections within these galaxies (Ehrenfreund et al 2002;Cox et al , 2007Welty et al 2006;Bailey et al 2015;van Loon et al 2013), reaching up to several tens of lines of sight for the DIBs at λ5780 and λ5797. In both galaxies, DIBs seem weaker with respect to N(H i) and E(B − V) than in our Galaxy.…”

Section: Introductionmentioning

confidence: 99%

Diffuse interstellar bands λ5780 and λ5797 in the Antennae Galaxy as seen by MUSE

Monreal-Ibero

Weilbacher

Wendt

2018

A&A

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Context. Diffuse interstellar bands (DIBs) are faint spectral absorption features of unknown origin. Research on DIBs beyond the Local Group is very limited and will surely blossom in the era of the Extremely Large Telescopes. However, we can already start paving the way. One possibility that needs to be explored is the use of high-sensitivity integral field spectrographs. Aims. Our goals are twofold. First, we aim to derive reliable mapping of at least one DIB in a galaxy outside the Local Group. Second, we want to explore the relation between DIBs and other properties of the interstellar medium (ISM) in the galaxy. Methods. We use Multi Unit Spectroscopic Explorer (MUSE) data for the Antennae Galaxy, the closest major galaxy merger. High signal-to-noise spectra were created by co-adding the signal of many spatial elements with the Voronoi binning technique. The emission of the underlying stellar population was modelled and substracted with the STARLIGHT spectral synthesis code. Flux and equivalent width of the features of interest were measured by means of fitting to Gaussian functions. Results. To our knowledge, we have derived the first maps for the DIBs at λ5780 and λ5797 in galaxies outside the Local Group. The strongest of the two DIBs (at λ5780) was detected in an area of ∼ 0.6 , corresponding to a linear scale of ∼ 25 kpc 2 . This region was sampled using >200 out of ∼1200 independent lines of sight. The DIB λ5797 was detected in >100 independent lines of sight. Both DIBs are associated with a region of high emission in the H i 21 cm line, implying a connection between atomic gas and DIBs, as the correlations in the Milky Way also suggest. Conversely, there is mild spatial association between the two DIBs and the molecular gas, in agreement with results for our Galaxy that indicate a lack of correlation between DIBs and molecular gas. The overall structures for the DIB strength distribution and extinction are comparable. Within the system, the λ5780 DIB clearly correlates with the extinction, and both DIBs follow the relationship between equivalent width and reddening when data for several galaxies are considered. This relationship is tighter when comparing only with galaxies with metallicities close to solar. Unidentified infrared emission bands (UIBs, likely caused by polycyclic aromatic hydrocarbons (PAHs)) and the λ5780 and λ5797 DIBs show similar but not identical spatial distributions. We attribute the differences to extinction effects without necessarily implying a radically different nature of the respective carriers. Conclusions. The results illustrate the enormous potential of integral field spectrographs for extragalactic DIB research.

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Mapping atomic and diffuse interstellar band absorption across the Magellanic Clouds and the Milky Way

Cited by 22 publications

References 46 publications

Thermal Pressures in the Interstellar Medium of the Magellanic Clouds*

Thermal Pressures in the Interstellar Medium of the Magellanic Clouds*

Probing the Local Bubble with diffuse interstellar bands

Diffuse interstellar bands λ5780 and λ5797 in the Antennae Galaxy as seen by MUSE

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