An Aromatic Inventory of the Local Volume

Abstract

Using infrared photometry from the Spitzer Space Telescope, we perform the first inventory of aromatic feature emission (AFE, but also commonly referred to as PAH emission) for a statistically complete sample of star-forming galaxies in the local volume. The photometric methodology involved is calibrated and demonstrated to recover the aromatic fraction of the IRAC 8µm flux with a standard deviation of 6% for a training set of 40 SINGS galaxies (ranging from stellar to dust dominated) with both suitable mid-infrared Spitzer IRS spectra and equivalent photometry. A potential factor of two improvement could be realized with suitable 5.5µm and 10µm photometry, such as what may be provided in the future by JWST. The resulting technique is then applied to mid-infrared photometry for the 258 galaxies from the Local Volume Legacy (LVL) survey, a large sample dominated in number by low-luminosity dwarf galaxies for which obtaining comparable midinfrared spectroscopy is not feasible. We find the total LVL luminosity due to five strong aromatic features in the 8µm complex to be 2.47 × 10 10 L ⊙ with a mean volume density of 8.8 × 10 6 L ⊙ Mpc −3 . Twenty-four of the LVL galaxies, corresponding to a luminosity cut at M B = −18.22, account for 90% of the aromatic luminosity. Using oxygen abundances compiled from the literature for 129 of the 258 LVL galaxies, we find a correlation between metallicity and the aromatic to total infrared emission ratio but not the aromatic to total 8µm dust emission ratio. A possible explanation is that metallicity plays a role in the abundance of aromatic molecules relative to the total dust content, but other factors such as star formation and/or the local radiation field affect the excitation of those molecules.

Coevolution of metallicity and star formation in galaxies toz≃ 3.7 – I. A Fundamental Plane

“…According to the results of Andrews & Martini (2013), who used a stacking technique to measure the oxygen abundances of ∼200 000 star-forming galaxies from the SDSS to enhance the signal-to-noise ratio of the weak [Oiii] Thus, in what follows, where there are no direct-Te estimates, we have applied the transformations given by Kewley & Ellison (2008) to convert the original strong-line O/H calibrations for the MEGA dataset (and SDSS10 sample) to the calibrations by D02 and PP04 (PP04N2, PP04O3N2). As reported in Table 1, the original O/H calibrations include: KD02 Cresci et al 2012;Mannucci et al 2010;Troncoso et al 2014); KK04 (Kobulnicky & Kewley 2004;Kennicutt et al 2011;Henry et al 2013;Xia et al 2012);M91 (McGaugh 1991;Marble et al 2010); PP04N2, PP04O3N2 (Pettini & Pagel 2004;Shapley et al 2004Shapley et al , 2005aLiu et al 2008;Yabe et al 2012;Zahid et al 2014;Steidel et al 2014); and T04 (Tremonti et al 2004;de los Reyes et al 2015). .…”

Cold H i in faint dwarf galaxies

“…Metallicity measurements are available only for a few of our sample galaxies (e.g. Marble et al 2010;Moustakas & Kennicutt 2006). For the rest of our galaxies, we use the MB-Z metallicity relation for dIrs from (Ekta & Chengalur 2010) to estimate their metallicity.…”

“…The total error in ΣSFR is calculated as the quadrature sum of the individual errors. Firstly, 1,2 Galaxies with detected cold HI in Gaussian decomposition and T B method respectively 3,4 Galaxies with available Hα and FUV map respectively References - † : (Marble et al 2010); ‡ : (Moustakas & Kennicutt 2006) we adopt a 10% calibration error in FUV flux and a 15% calibration error in Hα flux measurement. An additional error of ∼ 50% in star formation rate is expected due the variation in IMF and star formation history (Leroy et al 2012(Leroy et al , 2013.…”

The Spitzer Surveys of the Small Magellanic Cloud: Insights into the Life-Cycle of Polycyclic Aromatic Hydrocarbons

“…They found that at a metallicity of 12 + log(O/H) ∼ 8, galaxies transition from having a median q PAH ∼ 3.5%, similar to the Milky Way value of 4.6%, to a median of ∼1%. Spectroscopic (Wu et al 2006;Engelbracht et al 2008) and photometric investigations (Marble et al 2010) of large samples of low-metallicity galaxies provide clear evidence for this deficit.…”