\HI 21-cm Line Properties of the Nearby LIRG IRAS 04296+2923

Abstract

We present an analysis of archival Very Large Array (VLA) and Five-hundred-meter Aperture Spherical radio Telescope (FAST) \HI\ 21 cm data, together with archival multi-band radio continuum observations, of the nearby luminous infrared galaxy IRAS~04296+2923. The system, located behind the Taurus dark cloud at a distance of $\sim$29 Mpc, forms a small galaxy group consisting of five members as revealed by the \HI\ imaging. IRAS~04296+2923 has a close companion, HI~0432+2926, with a projected separation of $\sim$40 kpc, a small line-of-sight velocity difference of $Δ$ v = 26 km s$^{-1}$, and comparable total \HI\ masses of order $10^{9}$~$M_{\odot}$. Both galaxies exhibit regular \HI\ velocity fields and characteristic double-horn profiles in the VLA and FAST data, accompanied by only subtle asymmetries and extended \HI\ structures, indicating rotation-dominated kinematics with early signs of weak tidal interaction. Radio continuum emission is detected only from IRAS~04296+2923 and is confined to its nuclear region, consistent with previous studies. Modeling of its multi-band radio spectrum reveals a significant contribution from free--free emission at high frequencies ($>$30 GHz) and a high FIR-to-radio flux ratio ($q_{8.4}\simeq3.2$), implying a young, dust-obscured nuclear starburst. Taken together, the regular \HI\ kinematics, the small velocity offset, and the group-scale environment favor an interpretation in which IRAS~04296+2923 and HI~0432+2926 form a gravitationally bound, orbiting galaxy pair embedded in a small group, rather than an advanced merger. In this context, the luminous infrared galaxy (LIRG) nature of IRAS~04296+2923 is more plausibly driven by internal processes, such as bar-induced gas inflow, possibly modulated by long-timescale, low-level tidal interactions with nearby group companions.

Figures (19)

• Figure 1: H I emission contours overlaid on the optical Pan-STARRS images of IRAS 04296+2923 and the other members of its galaxy group. Red, blue, and black contours represent the combined H I total intensity (moment 0) maps from the VLA D-array, VLA C-array, and FAST observations, respectively. White contours in the upper-left panel indicate central H I absorption toward IRAS 04296+2923 as detected in the VLA C-array data. For the upper-left panel, the contour levels are: red: 0.03, 0.06, 0.12, 0.24, 0.48, 0.96, 1.30, and 1.54 Jy beam$^{-1}$ km s$^{-1}$; blue: 0.09, 0.18, and 0.36 Jy beam$^{-1}$ km s$^{-1}$; black: 0.10, 0.20, 0.40, 0.80, 1.60, and 3.20 Jy beam$^{-1}$ km s$^{-1}$; white (absorption): $-$0.30, $-$0.40, $-$0.50, and $-$0.60 Jy beam$^{-1}$ km s$^{-1}$. For the remaining panels, the contour levels are: red: 0.40, 0.80, and 1.60 Jy beam$^{-1}$ km s$^{-1}$; blue: 0.18, 0.36, and 0.72 Jy beam$^{-1}$ km s$^{-1}$; black: 0.10, 0.20, 0.40, 0.80, 1.60, and 3.20 Jy beam$^{-1}$ km s$^{-1}$. In all panels, the lowest contour corresponds to the $3\sigma$ level. White and red crosses mark the optical and H I centroid positions of the detected sources listed in Table \ref{['sources']}. Insets show zoomed-in optical views of the individual galaxies. The lower-left inset indicates the synthesized beam sizes for each dataset (see Table \ref{['table1']} for beam parameters).
• Figure 2: H I line profiles of IRAS 04296+2923 (left) and HI 0432+2926 (right) obtained from the VLA-C, VLA-D, and FAST observations. For IRAS 04296+2923, the H I emission lines were extracted from a circular region with a diameter of 3.4, centered at $\mathrm{RA}=04^{\mathrm{h}}32^{\mathrm{m}}48.9^{\mathrm{s}}$, $\mathrm{Dec}=+29^{\circ}29^{\prime}53.1^{\prime\prime}$. The H I absorption spectrum was obtained from a box region centered at $\mathrm{RA}=04^{\mathrm{h}}32^{\mathrm{m}}48.6^{\mathrm{s}}$, $\mathrm{Dec}=+29^{\circ}29^{\prime}57.4^{\prime\prime}$, with a size of about 20$\times$ 20. The black line represents the Nançay H I data from 1995AA...299..347C. For HI 0432+2926, the H I emission lines were extracted from a box region centered at $\mathrm{RA}=04^{\mathrm{h}}32^{\mathrm{m}}33.7^{\mathrm{s}}$, $\mathrm{Dec}=+29^{\circ}26^{\prime}26.5^{\prime\prime}$, with a size of about 2.5$\times$ 4.1. Because the angular resolution of the FAST telescope is relatively low, the two galaxies cannot be fully separated in the FAST H I image. Therefore, the FAST H I line profiles were extracted from two box regions, as indicated in Fig. \ref{['fig:fast']}. In the left panel, the y-axis of the H I absorption line is shown on the right, while those of the emission lines are on the left.
• Figure 3: Velocity (moment-1) maps of IRAS 04296+2923 and HI 0432+2926. The upper left and right panels show the velocity fields derived from the VLA-D and VLA-C array data, respectively. The bottom panel presents the velocity map from the FAST H I survey data, with red contours representing the H I emission from the VLA-D project, as shown in Fig. \ref{['fig.1:HIpos']}. The synthesized beam of each observation is shown in the lower left corner of each panel.
• Figure 4: PV diagrams of IRAS 04296+2923 generated from the H I cube images observed with the VLA-D (left) and VLA-C (right) configurations, using the 3D-BAROLO fitting software. The blue contours show the observed data, while the red contours indicate the best-fit model results. The yellow dots mark the fitted rotation curve derived from the model. The angles ($\phi$) in the upper-right corners denote the position angles obtained from the kinematic fitting. The grey contour at the center of the right panels highlights the region where strong H I absorption is detected in the C-configuration data.
• Figure 5: Integrated intensity (moment 0) map of IRAS 04296+2923 (upper left) and H I 0432+2926 (lower right), derived from the VLA–D array H I data using SoFiA. The white contours show the 3$\sigma$ H I emission from the same VLA–D data, identical to those displayed in Fig. \ref{['fig.1:HIpos']}. Region 11 (green box) covers an area of 3$\times$ 2, while Region 10 (green circle) covers 100$\times$ 100. The corresponding H I spectral profiles extracted from these regions are presented in Fig. \ref{['fig:regionline']}, and the fitted parameters are summarized in Table \ref{['region']}.