The Competing Influence of Ram Pressure and Tidal Interaction in NGC 2276

TL;DR

This paper investigates whether ram-pressure stripping (RPS) or tidal interactions primarily shape the morphology of NGC 2276, a member of the NGC 2300 group. Using new high-resolution HST WFC3/UVIS imaging across five filters, complemented by Spitzer IRAC data, Calar Alto PMAS/PPAK Hα maps, and NOEMA CO observations, the authors map the distribution of young and old stellar populations, gas, and dust. They find that blue/UV and Hα emission are asymmetric and preferentially located on the leading side, while the old stellar disk remains relatively intact, and they detect spiral-arm unwinding with pitch angles increasing with radius, both consistent with strong RPS effects. While tidal interactions with NGC 2300 are not excluded, the multiwavelength evidence favors RPS as the dominant mechanism driving NGC 2276’s peculiar morphology, with future SED-based stellar population separation and hydrodynamical simulations planned to quantify any tidal contribution.

Abstract

The evolution of galaxies in groups is profoundly influenced by a variety of physical processes, with ram pressure and tidal interactions playing pivotal roles in shaping their structural and evolutionary pathways. The relative influence of these two processes is still debated in groups compared to clusters, as ram pressure is less understood there. We study NGC 2276, a nearby galaxy (z$\sim$0.0079) where the dominant process is still an open question. We examine the distribution of stellar populations in NGC 2276 using multiwavelength data to assess potential evidence of tidal interactions and ram-pressure stripping. We present the first HST WFC3/UVIS images of NGC 2276, and use them to investigate the distribution of stellar populations across the disk of NGC 2276, where we assume that the bluer broadband filters mainly trace younger stellar populations, while the redder filters trace mainly older stellar populations. Furthermore, by comparing HST images with maps of H$α$ emission from Calar Alto's PMAS/PPAK integral field unit (IFU) and near-IR maps from Spitzer's IRAC, we identify arm-like overdensity features that trace the spiral structure of this galaxy and tracked the variation of their pitch angle with radius. Our results indicate that the distribution of the stellar populations is asymmetrical. The youngest stellar populations (up to $\sim$100 Myr) show higher concentration on the leading side of the galaxy and are more diffuse on the trailing side, consistent with gas compression due to ram-pressure. This asymmetry is visible in the red filters as well. We also show that the average pitch angles of the overdensity features increase with galactocentric distance. Our findings are consistent with the fact that ram pressure is the leading mechanism for the peculiar morphology of NGC 2276, but do not exclude the possibility that tidal interactions could have played a role.

Figures (10)

• Figure 1: Stellar mass surface density map of the center of NGC 2300 group obtained by combining Spitzer's IRAC 1 and IRAC 2 images using stellar mass relation from querejeta. Red cross shows the group X-ray IGM emission center from mulchaey. LOFAR contours of the radio continuum emission roberts at 144 MHz (3, 6, 12, 24, 48, 96, 192×RMS, RMS = 60$\mu$Jy, resolution = 4.9 $\times$ 4.3 arcsec$^2$) shown overplotted in white. Golden arrow shows the predicted trajectory of NGC 2276, derived from the direction of the radio continuum tail Souchereau2025, and the H$\alpha$ kinematics Haan2014.
• Figure 2: Top: color-composite HST image of NGC 2276. The combination of filters used as RGB channels are indicated with corresponding colors on the bottom right. See text for details on the relative weights used for each filter. Bottom Right: Zoomed in view of the southwestern side of NGC 2276 (Region A) showing disk truncation and the presence of dust. Bottom Left: Zoomed in view of the southern side of NGC 2276 (Region B) showing isolated clumps of young stars.
• Figure 3: 3-$\sigma$ S/N level contours for different HST filters of NGC 2276. The background grayscale image shown in each panel is the H$\alpha$ moment-0 map extracted from the Calar Alto IFU data. The bottom right panel is the color image, expressed as $\log_{10}\left( \mathrm{F275W/F814W}\right)$, smoothed and reprojected to the same resolution as H$\alpha$ map. Yellow rectangle shows approximately the region affected by the scattered light anomaly fowler.
• Figure 4: Location of the NGC 2276 center, shown in different tracers. Red cross marks the coordinates of the center. Panel a shows the RGB composite from Fig. \ref{['fig:RGB']}, panels b-f show HST UVIS/WFC3 filters from NUV to NIR. Panel g shows CO map from the IRAM NOEMA dataset, and in the panel h, the velocity map from PMAS/PPAK map of H$\alpha$ is shown tomicic18, along with the black contour depicting the systemic velocity of 2416 km/s.
• Figure 5: Intensity profiles of NGC 2276 as a function of galactocentric radius. Top: F555W image divided in 8 sectors with constant azimuthal separation of 45°. The concentric ellipses show regions with constant galactocentric distance of 3, 6, 9 and 12 kpc. White dotted line represents 3-$\sigma$ background noise level contour. Bottom: Surface brightness radial profile in the F555W band for each of the 8 sectors in bin size of 0.5 kpc. Three dotted lines represent 1,2, and 3-$\sigma$ background noise level. All data points have S/N above 5.