The spatially resolved stellar population and ionized gas properties in the merger LIRG NGC 2623

Abstract

We report on a detailed study of the stellar populations and ionized gas properties in the merger LIRG NGC 2623, analyzing optical integral field spectroscopy from the CALIFA survey and PMAS LArr, multiwavelength HST imaging, and OSIRIS narrow band Hα and [NII]λ6584 imaging. The spectra were processed with the starlight full spectral fitting code, and the results are compared with those for two early-stage merger LIRGs (IC 1623 W and NGC 6090), together with CALIFA Sbc/Sc galaxies. We find that NGC 2623 went through two periods of increased star formation (SF), a first and widespread episode, traced by intermediate-age stellar populations ISP (140 Myr-1.4 Gyr), and a second one, traced by young stellar populations YSP (<140 Myr), which is concentrated in the central regions (<1.4 kpc). Our results are in agreement with the epochs of the first peri-center passage (∼200 Myr ago) and coalescence (<100 Myr ago) predicted by dynamical models, and with high-resolution merger simulations in the literature, consistent with NGC 2623 representing an evolved version of the early-stage mergers. Most ionized gas is concentrated within <2.8 kpc, where LINER-like ionization and high-velocity dispersion (∼220 km s −1 ) are found, consistent with the previously reported outflow. As revealed by the highest-resolution OSIRIS and HST data, a collection of HII regions is also present in the plane of the galaxy, which explains the mixture of ionization mechanisms in this system. It is unlikely that the outflow in NGC 2623 will escape from the galaxy, given the low SFR intensity (∼0.5 M ⊙ yr −1 kpc −2 ), the fact that the outflow rate is three times lower than the current SFR, and the escape velocity in the central areas is higher than the outflow velocity.

The spatially resolved star formation history of mergers

“…The most advanced merger in our sample, NGC 2623, which has already passed coalescence, seems to reproduce the predictions from simulations, showing both an extended SFR enhancement about 1 Gyr ago, relic of the first pericentre passage epoch, and a current SFR enhancement in the last 30 Myr, located in the central 0.5 HLR but not in the outer parts, consistent with the second pericentre passage and final coalescence. This is consistent with what we already found through the stellar population analysis in this system (Cortijo-Ferrero et al 2017b). We note that advanced postcoalescence systems are ideal places where to apply the fossil method to unveil past star formation epochs, as both the extended and nuclear starbursts should be identifiable in the spectra of most of these systems if the current merger scenario is correct.…”

“…On the contrary, in NGC 2623 there is a slight increase of the SFR in this longest time scale, which is a factor of approximately three larger than in Sc MSSF galaxies. This is expected given the known presence and relevance of intermediate-age stellar populations in this system (Cortijo-Ferrero et al 2017b).…”

“…Thus, they constitute a suitable sample for this pilot study that will be extended in the future for a larger CALIFA sub-sample. Based on IFS data, a detailed analysis on the spatially resolved stellar population properties for IC 1623 and NGC 6090 are presented in Cortijo-Ferrero et al (2017a), for NGC 2623 in Cortijo-Ferrero et al (2017b), and for the Mice in Wild et al (2014). The main properties of the sample are summarized in Table 1.…”

A Review of Recent Observations of Galactic Winds Driven by Star Formation

“…This is true both at ground-based resolution and with enhanced spatial resolution from adaptive optics; the latter is important for probing the nuclear regions of galaxies where GWs emerge from their power sources. Studies of one or a few galaxies with stellar GWs published in the current decade are numerous [55][56][57][58][59][60][61][62][63][64]. These detailed case studies highlight the ubiquity and complex, multiphase nature (ionized, neutral, dusty) of these winds ( Figure 2) and the power of IFS for leveraging the combination of spectral and spatial information to separate outflows from their hosts.…”

Comprehensive Broadband X-ray and Multiwavelength Study of Active Galactic Nuclei in Local 57 Ultra/luminous Infrared Galaxies Observed with NuSTAR and/or Swift/BAT

“…Ultrafast outflow (UFO), an extremely fast (∼0.1-0.3c) and highlyionized wind emanating from a close vicinity (∼10 −2 pc) of an SMBH, is seen as X-ray blueshifted absorption lines in some U/LIRGs (e.g., Tombesi et al 2015;Feruglio et al 2015;Mizumoto et al 2019). On kpc scales, fast (an order of 1000 km s −1 ) and massive outflow of ionized gas has been discovered by deep optical/near-IR spectroscopy mainly from integral field observations (IFU; e.g., Fischer et al 2013;Rich et al 2015;Cortijo-Ferrero et al 2017a;Toba et al 2017a;Kakkad et al 2018;Venturi et al 2018;Smith et al 2019;U et al 2019;Boettcher et al 2020;Fluetsch et al 2021). At the far-IR and millimeter/submillimeter wavelengths, molecular outflow, a cold gas wind with a size of ∼400 pc and a velocity of ∼500 km s −1 , is observed in many U/LIRGs (e.g., Spoon et al 2013;Veilleux et al 2013;Cicone et al 2014;González-Alfonso et al 2017;Laha et al 2018 and the references therein; Lutz et al 2020; but see e.g., Toba et al 2017b).…”