[Paper Review] Towards DIB mapping in galaxies beyond 100 Mpc. A radial profile of the $λ$5780.5 diffuse interstellar band in AM 1353-272 B

A. Monreal‐Ibero, Peter M. Weilbacher+6 more|GoeScholar The Publication Server of the Georg-August-Universität Göttingen (Georg-August-Universität Göttingen)|Feb 23, 2015

Astrophysics and Star Formation Studies32 references10 citations

TL;DR

This study presents the first spatially resolved mapping of the diffuse interstellar band (DIB) at λ5780.5 in a galaxy beyond the Local Group—AM 1353-272 B—using MUSE integral field spectroscopy. By co-adding 568 spatially resolved spectra across 13.5 kpc², it demonstrates a radial decrease in DIB equivalent width correlated with interstellar extinction, confirming a global DIB-extinction relationship in an external spiral galaxy for the first time.

ABSTRACT

Diffuse Interstellar Bands (DIBs) are non-stellar weak absorption features of unknown origin found in the spectra of stars viewed through one or several clouds of Interstellar Medium (ISM). Research of DIBs outside the Milky Way is currently very limited. Specifically spatially resolved investigations of DIBs outside of the Local Group is, to our knowledge, inexistent. Here, we explore the capability of the high sensitivity Integral Field Spectrograph, MUSE, as a tool to map diffuse interstellar bands at distances larger than 100 Mpc. We use MUSE commissioning data for AM 1353-272 B, the member with highest extinction of the "The Dentist's Chair", an interacting system of two spiral galaxies. High signal-to-noise spectra were created by co-adding the signal of many spatial elements distributed in a geometry of concentric elliptical half-rings. We derived decreasing radial profiles for the equivalent width of the $λ$5780.5 DIB both in the receding and approaching side of the companion galaxy up to distances of $\sim$4.6 kpc from the center of the galaxy. Likewise, interstellar extinction, as derived from the Halpha/Hbeta line ratio displays a similar trend, with decreasing values towards the external parts. This translates into an intrinsic correlation between the strength of the DIB and the extinction within AM 1353-272 B consistent with the current existing global trend between these quantities when using measurements for both Galactic and extragalactic sight lines. Mapping of DIB strength in the Local Universe as up to now only done for the Milky Way seems feasible. This offers a new approach to study the relationship between DIBs and other characteristics and species of the ISM in different conditions as those found in our Galaxy to the use of galaxies in the Local Group and/or single sightlines towards supernovae, quasars and galaxies outside the Local Group.

Motivation & Objective

• To demonstrate the feasibility of spatially resolved DIB mapping in galaxies beyond 100 Mpc using high-sensitivity integral field spectroscopy.
• To investigate the spatial distribution of the λ5780.5 DIB in AM 1353-272 B, a low-luminosity, high-extinction spiral galaxy at 159 Mpc.
• To test whether the known correlation between DIB strength and interstellar extinction holds in an external galaxy with conditions different from the Milky Way.
• To explore the potential of MUSE and similar instruments for future large-scale DIB mapping in the Local Universe.
• To provide a new methodological framework for studying DIB-ISM relationships beyond single-line-of-sight measurements.

Proposed method

• Acquired MUSE integral field spectroscopy of AM 1353-272 B during commissioning runs with a 1×1 arcmin field of view and R≈2800 spectral resolution.
• Created high signal-to-noise spectra by co-adding signals from 568 spatial elements distributed in concentric elliptical half-rings across the galaxy.
• Measured the equivalent width (EW) of the λ5780.5 DIB in six distinct regions of the galaxy, spanning up to ~4.6 kpc from the center.
• Calculated interstellar extinction using the Hα/Hβ line ratio to derive E(B-V) values across the galaxy.
• Compared the radial profiles of DIB EW and extinction to assess their correlation in an external galaxy.
• Compiled and compared the DIB-extinction data with existing Galactic and extragalactic sightlines to assess consistency with the global trend.

Experimental results

Research questions

• RQ1 Can the λ5780.5 diffuse interstellar band be spatially resolved and mapped in a galaxy beyond the Local Group using integral field spectroscopy?
• RQ2 Does the strength of the DIB in AM 1353-272 B correlate with interstellar extinction across its disk, as observed in the Milky Way?
• RQ3 How does the DIB-extinction relationship in AM 1353-272 B compare to that observed in other galaxies, including those in the Local Group and in the Magellanic Clouds?
• RQ4 To what extent do environmental factors such as metallicity, radiation field, and star formation activity modulate the DIB-extinction correlation in external galaxies?
• RQ5 Can high-sensitivity instruments like MUSE enable 2D DIB mapping in the Local Universe, opening new avenues for studying DIB carriers?

Key findings

• The equivalent width of the λ5780.5 DIB decreases radially from the center of AM 1353-272 B, with a profile declining up to ~4.6 kpc from the galactic center on both the approaching and receding sides.
• The interstellar extinction, derived from the Hα/Hβ line ratio, shows a similar radial decrease, indicating lower dust content in the outer regions of the galaxy.
• A strong correlation is observed between the DIB equivalent width and extinction (E(B-V)) across AM 1353-272 B, with a constant ratio within measurement uncertainties.
• The DIB-extinction relationship in AM 1353-272 B aligns with the global trend observed in the Milky Way and M31, particularly when considering resolved studies of spiral galaxies.
• The data for AM 1353-272 B extend the DIB-extinction relation toward higher equivalent widths and E(B-V) values, consistent with the trend seen in other disk-like galaxies.
• The study confirms that 2D DIB mapping in galaxies beyond the Local Group is feasible with current high-sensitivity integral field spectrographs like MUSE.