The stellar edge of NGC 1494 with LSST Data Preview 1
Abstract
Galaxy size traces how galaxies grow and evolve, yet traditional metrics like the effective radius are biased metric as they mainly capture the concentration of light of a galaxy. A more accurate size proxy is the stellar edge: the outermost region of in situ star formation, shaped by gas density thresholds. Thanks to the depth of LSST Data Preview 1, we can now move beyond 1D profiles to 2D spatial analyses previously unattainable. We present an innovative way of processing DP1 raw data tailored to recover low surface brightness features, avoiding over subtraction of standard coadds. Applying it to multi-band ComCam data of NGC 1494, we detect a clear stellar edge at ~13 kpc, where the stellar mass surface density drops to ~1 M⊙/pc², which is consistent with theoretical thresholds for in situ star formation. This approach reveals structural 2D asymmetries at the stellar edge of NGC1494 and demonstrates the power of LSST to probe galaxy sizes in the era of wide-deep surveys.
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LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST Data Preview 1 Giulia Golini
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST DP1 NGC 1494, DECaLS DR10, FoV: 6' x 8' Gas density threshold of 3–10 M⊙/pc2 (Schaye 2004) ΛCDM inside out growth of galaxies (Peebles 1969); Gas converted into stars (in situ star formation) Stellar mass density drop at 1–3 M⊙/pc2
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST DP1 µV > 27 mag/arcsec2 ΛCDM inside out growth of galaxies (Peebles 1969); Gas converted into stars (in situ star formation) NGC 4565; Martinez-Lombilla+2019 Gas density threshold of 3–10 M⊙/pc2 (Schaye 2004) Stellar mass density drop at 1–3 M⊙/pc2 µ[mag arcsec-2]
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST DP1 R1(Trujillo+2020); Redge (Chamba+2022); radial location of the stellar mass density drop Stripe82 data; Chamba+2022 Redge ∝ M★1/3 at z = 0 Redge evolution (5000 km/h) and 𝛴★edge decrease since z = 1 Buitrago & Trujillo 2023
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST DP1 Buitrago & Trujillo 2023 R1(Trujillo+2020); Redge (Chamba+2022); radial location of the stellar mass density drop ! WARNING ! Redge was visually identified Stripe82 data; Chamba+2022
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms Euclid (1.2m) LSST (6.4m) The stellar edge of NGC 1494 with LSST DP1 ! WARNING ! Redge was visually identified In the era of big data we must avoid visual identification of the edge
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST DP1 Golini+2025 Redge: As the minimum of the second derivative of 𝛴★ approximated by a BrokenExponential function NGC 3486 LBT, 8.2m, µ(lim)~31 mag/arcsec2 V-band (3σ; 10" x 10") In the era of big data we must avoid visual identification of the edge
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST DP1 NGC 3486 Golini+2025 In the era of big data we must avoid visual identification of the edge Schaye 2004 ✅ Redge: As the minimum of the second derivative of 𝛴★ approximated by a BrokenExponential function LBT, 8.2m, µ(lim)~31 mag/arcsec2 V-band (3σ; 10" x 10")
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST DP1 In the era of big data we must avoid visual identification of the edge What about using LSST? LSST (6.4m), µ(g, lim)~30.3 mag/arcsec2 (3σ; 10"x10") in 10 years Redge: As the minimum of the second derivative of 𝛴★ approximated by a BrokenExponential function
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms Future work: - Improved gain correction The stellar edge of NGC 1494 with LSST DP1 LSST DP1, 16 channels GMOS camera at Gemini telescopes; Golini+2024 µ(g,lim (3σ; 10"x10")) ~30.9 mag/arcsec2 2DO 0RGO 5GDO 1
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST DP1 Future work: - Improve gain correction - Test running flat-field correction - Weighted coadd - Add visits to increase depth - PSF removal - multi-wavelength analysis LSST (6.4m), expected µ(g,lim)~30.3 mag/arcsec2 (3σ; 10"x10") in 10 years
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST DP1 To warp up: - Galaxy edges are key to testing ΛCDM inside-out growth → require deep imaging - LSST will deliver the depth and coverage needed for multi-wavelength and statistical studies - Optimized data reduction is essential to reach full potential LSST (6.4m), expected µ(g,lim)~30.3 mag/arcsec2 (3σ; 10"x10") in 10 years
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The stellar edge of NGC 1494 with LSST Data Preview 1 Giulia Golini