A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE).XII. Ionised gas emission in the inner regions of lenticular galaxies

Abstract

As part of the Virgo Cluster Survey Tracing Ionised Gas Emission (VESTIGE), a blind narrow-band Hα+ [NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT, we discovered eight massive (10 10 M star 10 11 M ) lenticular galaxies with prominent ionised gas emission features in their inner (few kpc) regions. These features are either ionised gas filaments similar to those observed in cooling flows (2 galaxies), or thin discs with sizes 0.7 R(Hα) 2.0 kpc (6 galaxies), thus significantly smaller than those of the stellar disc (R(Hα) 7-22 % R iso (r)). These discs have morphological properties similar to those of the dust seen in absorption in high-resolution HST images. Using a unique set of multifrequency data, including new or archival ASTROSAT/UVIT, GALEX, HST, CFHT, Spitzer, and Herschel imaging data, combined with IFU (MUSE, ALMA) and long-slit (SOAR) spectroscopy, we show that while the gas located within these inner discs is photoionised by young stars, signaling ongoing star formation, the gas in the filamentary structures is shock-ionised. These discs have a star formation surface brightness similar to those observed in late-type galaxies. Because of their reduced size, however, these lenticular galaxies are located below the main sequence of unperturbed or cluster star-forming systems. By comparing the dust masses measured from absorption maps in optical images, from the Balmer decrement, or estimated by fitting the UV-to-far-IR spectral energy distribution of the target galaxies, we confirm that those derived from optical attenuation maps are heavily underestimated because of geometrical effects due to the relative distribution of the absorbing dust and the emitting stars. We have also shown that these galaxies have gas-to-dust ratios of G/D 80 320 30 , and that the star formation within these discs follows the Schmidt relation, albeit with an efficiency reduced by a factor of ∼ 2.5. Using our unique set of multifrequency data, we discuss the possible origin of the ionised gas in these objects, which suggests multiple and complex formation scenarios for massive lenticular galaxies in clusters.

Probing multiphase gas in local massive elliptical galaxies via multiwavelength observations

“…Low level detection at far-IR wavelengths accounts for a mere 3500 M of total dust estimated with the spectral energy distribution (SED) modeling software, CIGALEMC (Amblard et al 2014), although larger dust masses are reported in a recent paper by Boselli et al (2021). Even if specific SED fitting codes could generate slightly different dust masses (similarly to Boselli et al (2021), in this work we have used results, among others, derived from CIGALE SED code (see section 4 and discussion in Amblard et al 2014)), we believe that most of the dust mass discrepancy is due to the evaluation of the diffuse and extended FIR emission that is given as input to the SED fitting process. There is indeed a significant difference between the two FIR sets of data (see Table 7, and Ciesla et al 2012;Cortese et al 2014).…”

“…Early ground-based observations have reported Hα+[NII] emission in the central regions (Trinchieri & di Serego Alighieri 1991;Macchetto et al 1996). More recent very deep narrowband Hα+[NII] imaging carried out with MegaCam at the CFHT shows a diffuse and filamentary distribution of the ionised gas (Boselli et al 2021). X-ray emission is detected at the center of the galaxy with a sharp edge 3.1 kpc to the north, a cool (kT = 0.51 +0.09 −0.06 keV) tail extending 10 kpc to the south of the galaxy, and two 3 kpclong "horns" extending south on the sides of the north edge (Figure 11).…”

“…On one hand the non-detections in the [CII] emitting gas as well as in the CO line indicate that the cold gas reservoir, if present, it is not large. On the other hand, because of the non-detection in the CO line emission, Boselli et al (2021) estimate a mass of molecular gas Log M H2 = 8.63 M derived from the total dust mass and a gas-to-dust ratio of 80, rather than using the canonical conversion from equation 1. We regard NGC 4552 as a system with low cold gas content, however given the inconsistent data available on the derived molecular gas mass, a note of caution is advised.…”

The relation between accretion rate and jet power in early-type galaxies with thermally unstable hot atmospheres

“…Masses for all other galaxies were taken from direct measurements of gas or star kinematics from within the sphere of influence of the SMBH. 𝑑 In the case of NGC 4552, the H𝛼+[N ] morphology was taken from Boselli et al (2021).…”