Enigmatic Emission Structure around Mrk 783: Cross-Ionization of a Companion 100 kpc Away

Round 1

Reviewer 1 Report

see attached file

Comments for author File: Comments.pdf

Author Response

The authors are grateful to the anonymous reviewer for his/her valuable remarks.

We have corrected grammatical mistakes and improved the result using the new  analysis of the [SII] lines flux ratio.  The important corrections are marked in bold.

Reviewer 2 Report

This manuscript reports deep [OIII], r band imaging and long slit spectroscopic observation of a narrow-line Seyfert 1 galaxy Mrk 783, to understand the origin of emission knots and the large-scale ionized gas emission. The authors performed detailed line diagnostics and kinematics analysis. Together with previous radio studies in the literature, they suggest that part of the satellite galaxy located at ~100 kpc (projected) distance is ionized by Mrk 783 as it falls in the ionizing cone. In this scenario Mrk 783 can be considered as ‘Hanny’s Voorwerp precursor’ that switches from radio-loud to radio-quiet nuclear activity.

Overall the paper presents significant new observational results and is well organized. I find the proposed case of cross-ionization interesting, but am not fully convinced that it is necessary to explain the data. The main issue is that there seems no evidence for deficit in ionizing continuum, i.e., aion ≈ 1 in the SE-knot and 0.12 in the outer disk of the companion galaxy. The authors suggested that “it is in the moment before falling of its ionization luminosity”. However, put the satellite aside, the ionization properties of Mrk 783 are quite typical of EELR of Seyferts. The Eddington ratio of 0.11 is in fact not that low, typical of radiative mode (compared to <10^-3 for radio mode). Can the authors please derive the typical electron density of the knots and the outer part of the satellite using SII lines? Since the satellite is much further away, if the satellite is ionized by Mrk 783, the density of the gas could be quite different to remain highly excited.

Figure 1: Please explain what bands are the color survey image.

Figure 6: Define the color bars.

Please correct some typos and improve the language in the manuscript. For example:

Title: “in 100 kpc away”

Line 4: exited-> excited

Line 8: falls to -> falls in

Line 10 radio-load -> loud

Line 50: the second “Omega=0.31”

Line 214: starformation

Author Response

The authors are grateful to the anonymous reviewer for his/her valuable remarks.

1) We have corrected grammatical mistakes and improved the result using the new  analysis of the [SII] ratio.   The important corrections are marked in bold. 

2) Thank you for drawing our attention to the electron density measurement. We found that the sulfur doublet was affected by atmospheric absorption in H2O telluric band. We have tried to correct our spectra for this absorption feature using the spectrum of the standard star (see sec 2). As a result, the intensity of the [SII] lines has changed and we corrected Figures 3 – 6 in accordance with the renewed data. Also, we gave estimations of the electron density in the article. Unfortunately, at the satellite outer parts emission lines intensity is too low for more confident conclusions about gas ionization state. This fact was commented on in Sec 4.

3) We agree with the reviewer that we don't have enough data for the firm conclusions that the ionizing radiation did not change during travel-light time from the Mrk~783 nucleus to the SE-knot and to the disk of SDSS~J1302+1625. See new comments in Sec 6.

Round 2

Reviewer 2 Report

The authors have carefully considered my suggestions and measured the key values.