NGC3521 as the Milky Way analogue: spectral energy distributon from UV to Radio and photometric variability

TL;DR

This study analyzes NGC 3521 across multiple wavelengths, confirming its LINER activity, detecting weak long-term photometric variability, and modeling its spectral energy distribution to derive galaxy properties.

Contribution

It provides the first evidence of weak nuclear variability in NGC 3521 and compares SED models with and without AGN contribution, favoring a non-active nucleus model.

Findings

Confirmed LINER nuclear activity.

Detected long-term photometric variability with BWB trend.

Derived galaxy properties including stellar mass, dust mass, and star formation rate.

Abstract

We studied the multiwavelength properties of NGC 3521, the Milky Way galaxy-twin, from UV- to radio, exploring the data from GALEX for UV-, SDSS for optical, 2MASS, WISE, MIPS (Spitzer) and PACS, SPIRE (Herschel) for IR-, and NRAO VLA for radio ranges. To obtain the spectral energy distribution (SED), we exploited the CIGALE software and constructed SEDs without (model A) and with (model B) AGN module. The type of nuclear activity of NGC 3521 is confirmed as the LINER. We also present the results of the photometric data processing. Exploring the ZTF observations in 2018-2024, we found, for the first time, a weak photometric variability of the nuclear activity, where the correlation between g-r color indices and g-magnitude for long-term timescale shows a BWB trend (bluer-when-brighter) with a Pearson coefficient r(g-r)=0.56, which is a medium correlation. To detect the variability of NGC 3521 during the day (IDV), we provided observations using a Zeiss-600 telescope with an aperture size of 8" at the Terskol observatory. The data obtained in the R-filter with an exposure of 90 sec for three hours on Feb 11, 2022, serve in favor of a trend towards an increase in brightness with the amplitude of variability of 0.04 +- 0.001 mag. According to the results of the simulations, the best fit to the observed SED is provided by model A, which considers the contribution to the radiation from all galaxy components, assuming that the galaxy nucleus is inactive. Within this model, we derived the stellar mass M$_{star}$ = 2.13 * 10$^{10} M_{Sun}$, the dust mass M$_{dust}$ = 8.45 * 10$^{7} M_{Sun}$, and the star formation rate SFR = 1.76 $M_{Sun}$ * yr$^{-1}$ with $\chi^{2}$/d.o.f = 1.8. Also, based on the HIPASS radio data, we estimated the mass of neutral hydrogen to be M$_{HI}$ = 1.3 * 10$^{10} M_{Sun}$, which is an order of magnitude greater than the mass of the stellar component.