Markarian 817

Lore & Background

The nucleus of Markarian 817 is active, classified as Seyfert 1.5 or Seyfert 1.2 according to Koss et al. 2017. It sits in a barred spiral galaxy close to face-on, with evidence of dust along the bar from Hubble imagery. A study from February 2011 showed the active core varies strongly in X-rays and ultraviolet rays, with X-ray luminosity varying by a factor of ~40 over 20 years and UV continuum/emission lines varying by a factor of ~2.3 over 30 years.

A 2021 study revealed highly absorbed X-ray spectra and new blueshifted, broad, and narrow UV absorption lines, indicating a dust-free, ionized obscurer in the inner broad-line region. During the first 55 days of observation, the UV continuum and broad emission line variability decoupled; the next 42 days showed the correlation recovering as the galaxy entered a less obscured state. Short C IV and Lyα lags suggest the accretion disk extends beyond the UV broad-line region.

Further observations in 2022 showed the source flux had declined compared to a prior point in the 19-year mission. Deep XMM Newton and NuSTAR observations revealed a complex X-ray wind with neutral and ionized absorption zones, including three velocity components: v/c = 0.043 (+0.007,-0.003), v/c = 0.079 (+0.003,-0.0008), and v/c = 0.074 (+0.004,-0.005), suggesting the wind arises at radii smaller than the optical broad line region.

Reader's Guide

Markarian 817 is significant for its highly variable active nucleus and complex outflows, which provide insights into the dynamics of Seyfert galaxies. The galaxy's central black hole, with an estimated mass of (4.9±0.8)×10^7 solar masses, drives winds moving at many millions of kilometers per hour, cleaning interstellar gas and suppressing star formation. This behavior, described as a 'temper tantrum,' suggests the black hole shapes its host galaxy. The galaxy's inclusion in the AGN STORM 2 project, led by Edward M. Cackett from Wayne State University, underscores its importance for understanding AGN variability and accretion processes. Studies comparing Markarian 817 with NGC 7469 revealed time lags in broad emission lines consistent with Keplerian motion, with outflowing components indicated by larger time lags in the red wing than the blue wing. The detection of a structured ultra-fast outflow with three velocity components further highlights its role in studying AGN feedback and the connection between black hole activity and galaxy evolution.

Did You Know?

• Markarian 817 is located 456 million light-years from Earth in the constellation Draco.
• Its X-ray luminosity varies by a factor of ~40 over 20 years.
• The galaxy's ultra-fast outflow has three velocity components, including v/c = 0.043.