The Environments of Star-Forming Galaxies Detected in the SFACT Survey: Do Mergers and Interactions Drive the Star Formation?

Abstract

We conduct an environmental analysis around 167 star-forming galaxies (SFGs) detected by the Star Formation Across Cosmic Time (SFACT) survey over the redshift range 0.129 $\leq$ z $\leq$ 0.500. We use three environmental estimators to characterize the local galactic environments around the SFACT SFGs, on the scales of 100 kpc to several Mpc. We categorize these environments based on the relative clustering strength with respect to a deep environment comparison redshift sample. The SFACT SFGs tend to be less clustered than the environment comparison sample (ECS), with no significant change in relative clustering strengths over our redshift range. We find that any trends with the star-formation rates (SFRs) of the SFACT galaxies and their environments are likely related to their absolute magnitudes, a proxy for mass. Mergers and interactions with other luminous galaxies do not appear to be the primary driver of the star-formation activity seen within the SFACT SFGs.

Figures (27)

• Figure 1: Sky map illustrating the main regions being considered in this study. The blue circles have a diamter of 1° and highlight the six SFACT fields that overlap with HectoMAP. The red dots are for each SFACT galaxy. Each small black dot represents a galaxy in the environment sample, which consists mostly of HectoMAP but also includes SDSS DR17, and redshift surveys conducted by B22 and by the SFACT survey.
• Figure 2: Sky map illustrating the environment comparison samples for the H$\alpha$ (left) and the [O3] (right) redshift windows. Black dots represent galaxies within the spectroscopic redshift surveys and red dots represent the SFACT galaxies. The outer dashed red rectangles designate the environment comparison samples. The inner dashed red rectangles indicate the SFACT 48'x40' field of view for H$\alpha$ windows, while the [O3] field of view has been truncated at the HectoMAP decl. limit of 44.0°.
• Figure 3: We determine the completeness of the extended environment comparison sample for field KR 1791 as a function of r$_{petro,\ 0}$, for both the H$\alpha$ (left) and [O3] (right) redshift windows. In the top subplots, histograms binned by 0.2 magnitudes are plotted for the extended environment comparison sample with spectra (black) and the galaxies from SDSS with photometry (blue). In the bottom subplots, the completeness is the fraction of galaxies with spectra to galaxies with photometry.
• Figure 4: KR 1759 and KR 1791 pencil-beam diagrams. The large-scale structure across the field can be seen, from high-density regions to void-like regions. The $\Delta$R.A. and $\Delta$Decl. from the field centers are projected in Mpc-space versus distance. Black symbols represent the environment comparison sample, red points represent the SFACT sample. The black dashed lines are the HectoMAP decl. limits, the pink dashed lines are the SFACT field of view, and the vertical solid lines represent the redshift limits of each SFACT detection window.
• Figure 5: KR 1825 and KR 2005 pencil-beam diagrams. Descriptions of the plot are found in Figure \ref{['fig:pb_kr1791_kr1759']}. The large-scale structure across the field can be seen, from high-density regions to void-like regions.