[Paper Review] The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. II. Sensitivity of the survey and an Atlas of Synthetic Dwarf Galaxies

G. Beccari, M. Bellazzini+6 more|CINECA IRIS Institutial research information system (University of Pisa)|Apr 11, 2016

Galaxies: Formation, Evolution, Phenomena52 references3 citations

TL;DR

This paper evaluates the sensitivity of the SECCO survey—using deep imaging with the Large Binocular Telescope—to detect faint, low-surface-brightness stellar counterparts of compact high-velocity clouds (UCHVCs), simulating synthetic dwarf galaxies with old, metal-poor populations. It demonstrates detection limits down to μ_V,h ≈ 27.5 mag/arcsec² at distances up to 2.5 Mpc, confirming high sensitivity to ultra-faint and gas-rich dwarfs, and identifies potential Virgo cluster dSphs as validation of the survey’s capability.

ABSTRACT

SECCO is a survey devoted to the search for stellar counterparts within Ultra Compact High Velocity Clouds. In this contribution we present the results of a set of simulations aimed at the quantitative estimate of the sensitivity of the survey as a function of the total luminosity, size and distance of the stellar systems we are looking for. For all our synthetic galaxies we assumed an exponential surface brightness profile and an old and metal-poor population. The synthetic galaxies are simulated both on the images and on the photometric catalogs, taking into account all the observational effects. In the fields where the available observational material is of the top quality we detect synthetic galaxies as >=5 sigma over-densities of resolved stars down to muV,h=30.0 mag/arcsec2, for D<=1.5 Mpc, and down to muV,h~29.5 mag/arcsec2, for D<=2.5 Mpc. In the field with the worst observational material of the whole survey we detect synthetic galaxies with muV,h<=28.8 mag/arcsec2 out to D<=1.0 Mpc, and those with muV,h<=27.5 mag/arcsec2 out to D<=2.5 Mpc. Dwarf galaxies with MV=-10, with sizes in the range spanned by known dwarfs, are detected by visual inspection of the images up to D=5 Mpc independently of the image quality. In the best quality images dwarfs are partially resolved into stars up to D=3.0 Mpc, and completely unresolved at D=5 Mpc. As an independent test of the sensitivity of our images to low surface brightness galaxies we report on the detection of several dwarf spheroidal galaxies probably located in the Virgo cluster with MV<=-8.0 and muV,h<=26.8 mag/arcsec2. The nature of the previously discovered SECCO 1 stellar system, also likely located in the Virgo cluster, is re-discussed in comparison with these dwarfs. While specific for the SECCO survey, our study may also provide general guidelines for detection of faint stellar systems with 8m class telescopes.

Motivation & Objective

• To quantify the sensitivity of the SECCO survey to faint, low-surface-brightness stellar systems associated with compact high-velocity clouds (UCHVCs).
• To simulate synthetic dwarf galaxies with realistic properties (exponential profiles, old metal-poor populations) to test detection limits across varying distances and luminosities.
• To assess the impact of observational conditions (image quality, depth) on the detectability of faint stellar over-densities.
• To validate the survey’s sensitivity by detecting known faint dSphs in the Virgo cluster as a benchmark.
• To provide general guidelines for detecting faint stellar systems with 8m-class telescopes using deep imaging and photometric catalogs.

Proposed method

• Simulated synthetic dwarf galaxies with exponential surface brightness profiles and old, metal-poor stellar populations across a range of total V-band magnitudes, sizes, and distances.
• Injected synthetic galaxies into both real images and photometric catalogs, accounting for all observational effects including seeing, background noise, and photometric zero-point errors.
• Used 5σ significance threshold to define detection limits in surface brightness (μ_V,h) as a function of distance and image quality.
• Classified survey fields into high, medium, and low quality based on image depth and seeing, and computed detection thresholds separately for each.
• Performed visual inspection of images to assess resolution and detectability of dwarfs at increasing distances (up to 5 Mpc).
• Cross-matched survey results with known Virgo cluster dSphs (MV < -8.0, μ_V,h < 26.8 mag/arcsec²) to test sensitivity and validate detection capability.

Experimental results

Research questions

• RQ1 What is the minimum detectable surface brightness (μ_V,h) for synthetic dwarf galaxies in the SECCO survey across different distances and image quality conditions?
• RQ2 To what distance can real, unresolved dwarf galaxies with MV = -10.0 be detected via visual inspection of SECCO images?
• RQ3 How does image quality affect the detection threshold for faint stellar over-densities in deep imaging surveys?
• RQ4 Can the SECCO survey detect known faint dSphs in the Virgo cluster, and what does this imply for its sensitivity to ultra-faint, gas-rich dwarfs?
• RQ5 What constraints do non-detections of stellar counterparts in UCHVCs place on the stellar-to-HI mass ratio of potential dwarf galaxies?

Key findings

• In the highest-quality SECCO fields (~36% of the survey), synthetic galaxies are detectable as ≥5σ over-densities down to μ_V,h ≈ 30.0 mag/arcsec² at distances ≤1.5 Mpc, and down to μ_V,h ≈ 29.5 mag/arcsec² at ≤2.5 Mpc.
• In the worst-quality fields, detection is still possible for galaxies with μ_V,h ≤ 28.8 mag/arcsec² at ≤1.0 Mpc and μ_V,h ≤ 27.5 mag/arcsec² at ≤2.5 Mpc.
• Dwarf galaxies with MV = -10.0 and typical sizes are detectable via visual inspection up to 5 Mpc, regardless of image quality.
• In the best-quality images, dwarfs are partially resolved into stars up to 3.0 Mpc and fully unresolved at 5.0 Mpc.
• The survey successfully detects known faint dSphs in the Virgo cluster with MV < -8.0 and μ_V,h < 26.8 mag/arcsec², confirming its sensitivity to low-surface-brightness systems.
• Non-detection of stellar counterparts in UCHVCs implies that any associated stellar systems would have M_HI/M_* ≥ 10, a signature typical of extremely metal-poor galaxies (XMPs), suggesting potential gas-rich, star-poor dwarfs remain undetected.