ASTR 410 Problem Set 06 Solutions: Scaling Relations: Tully-Fisher and Galaxy Structure and Inference with Galactic Surveys: quantitative reasoning

Instructor solution key

Scoring overview

Problems 1–4 are worth 25 points each. Award credit for correct reasoning, units, reproducibility, and interpretation; separate arithmetic slips from conceptual errors.

Problem 1

Expected approach: define the observable and model, substitute the shared constants or CSV values, preserve units, and test the stated assumption. Accept algebraically equivalent derivations when the physical interpretation is correct.

Key: With L proportional to v^4, doubling speed predicts L2/L1 = 16.

Problem 2

Expected approach: define the observable and model, substitute the shared constants or CSV values, preserve units, and test the stated assumption. Accept algebraically equivalent derivations when the physical interpretation is correct.

Key: The result must include a labeled plot, a sensitivity comparison, and a provenance statement. A numerical answer without those elements is incomplete.

Problem 3

Expected approach: define the observable and model, substitute the shared constants or CSV values, preserve units, and test the stated assumption. Accept algebraically equivalent derivations when the physical interpretation is correct.

Key: The result must include a labeled plot, a sensitivity comparison, and a provenance statement. A numerical answer without those elements is incomplete.

Problem 4

Expected approach: define the observable and model, substitute the shared constants or CSV values, preserve units, and test the stated assumption. Accept algebraically equivalent derivations when the physical interpretation is correct.

Key: The result must include a labeled plot, a sensitivity comparison, and a provenance statement. A numerical answer without those elements is incomplete.

Common errors